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CBSE Questions for Class 9 Physics Motion Quiz 1 - MCQExams.com
CBSE
Class 9 Physics
Motion
Quiz 1
$$a$$. A boy moving on a bicycle with a speed of $$18~ km/h$$.
$$b$$. A fast runner running with a speed of $$10 ~m/s$$.
$$c$$. A scooter moving with a speed of $$800 ~m/min$$.
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$$c > b > a$$
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$$b > c > a$$
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$$a> b > c$$
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$$c > a > b$$
If a body undergoes retardation, its velocity
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increases
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decreases
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remains same
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may increase or decrease
Explanation
Retardation means negative acceleration. It is rate of decrease of velocity with time.
So, if a body undergoes retardation, its velocity decreases.
Match the situations given in column I with the possible curves in column II and select the correct option, from codes given
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(a) $$\rightarrow$$ (q), (b) $$\rightarrow$$ (8), (c) $$\rightarrow$$ (p). (d) $$\rightarrow$$ (r)
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(a) $$\rightarrow$$ (s,r). (b) $$\rightarrow$$ (q), (c) $$\rightarrow$$ (s), (d) $$\rightarrow$$ (p)
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(a) $$\rightarrow$$(q,s); (b) $$\rightarrow$$ (r), (c) $$\rightarrow$$ (p), (d) $$\rightarrow$$ (s)
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(a) $$\rightarrow$$(s), (b) $$\rightarrow$$ (q,p), (c) $$\rightarrow$$ (s), (d) $$\rightarrow$$ (r)
Speed-distance graph of an object in uniform motion which comes to rest suddenly is
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0%
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When a body moves in circular path with uniform speed, it's motion is called uniform circular motion
State whether, the given statement is True/False?
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True
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False
Explanation
The above statement is true as in uniform circular motion, a body revolves in circular orbit with constant speed.
What is the acceleration of the race car that moves at constant velocity of 300 km/hr ?
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73.32 $$m/sec^2$$.
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0
$$m/sec^2$$
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63.33
$$m/sec^2$$
.
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53.33
$$m/sec^2$$
.
Explanation
Since the car is moving with a constant velocity, so change in the velocity of car is zero i.e. $$\Delta v = 0$$
Acceleration of car $$a = \dfrac{\Delta v}{\Delta t} = 0 \ m/s^2$$
Two cars X and Y accelerate at the rate of 2 $$m/{s^2}$$ and 3 $$m/{s^2}$$ respectively from rest.The ratio of time taken by the cars X and Y is 4:5.In that given ratio of time interval if the distance travelled by car x is 100 km then the distance travelled by car y is:
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$$\frac{{1875}}{8}\;km$$
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$$\frac{{1875}}{2}\;km$$
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$$\frac{{1875}}{4}\;km$$
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$$\frac{{375}}{4}\;km$$
The speed-time graph of a particle moving along a fixed direction is shown in figure. Then which of the following are correct?
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distance travelled by particle in $$10$$ sec is $$60m$$
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average speed in $$10$$ sec in $$6m/s$$
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average speed between $$t=2,t=6$$ sec is $$9m/s$$
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average speed between $$t=2,t=6$$ sec is $$6m/s$$
A particle is moving in positive x-direction with initial velocity of $$10\ m/s$$ and uniform retardation such that it reaches the initial position after $$10\ s$$. The distance traversed by the particle in $$6\ s$$ is
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$$24 m$$
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$$25 m$$
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$$26 m$$
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$$27 m$$
If a bus travelling at $$20\ m/s$$ is subject to a steady deceleration of $$5\ m/s^{2}$$, how long will it take to come rest?
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400 s
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0.4 s
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40 s
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4 s
Explanation
Using first equation of motion
$$ v= u+at$$, we have
$$ 0=20 +(-5)t$$
$$\Rightarrow 5t=20$$
$$\Rightarrow t=4s$$
The units of speed and velocity are the same in SI system.
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True
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False
Explanation
$$Speed= \dfrac{distance}{time}$$
$$velocity= \dfrac{displacement}{time}$$
The SI unit of distance and displacement is $$\text{meter}\ (m)$$. The SI unit of time is $$\text{second}\ (s)$$.
Therefore, the SI unit of speed and velocity is $$m/s$$
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Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
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Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
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Assertion is correct but Reason is incorrect
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Reason is correct but assertion is incorrect
Explanation
In the case of uniform circular motion, the acceleration of the body is constant and is always towards the center of the circular path. Here, the body moves in a curve, not in a straight line. So, the given assertion is incorrect.
A body with constant acceleration will speed up. For example, a freely falling body has a constant acceleration $$g$$. Its speed increases as it is falling down. So, the given reason is correct.
If the displacement of an object is proportional to square of time, then the object moves with
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uniform velocity
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uniform acceleration
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increasing acceleration
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decreasing acceleration
Explanation
When the rate of change of velocity with time of a body is constant then the object is said to be uniformly accelerated.
Or in other words in uniform acceleration, the displacement of an object is proportional to square of time.
The time taken by a vertically projected body before reaching the ground is:
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directly proportional to initial velocity
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directly proportional to square of initial velocity
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inversely proportional to square of initial velocity
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inversely proportional to initial velocity
Explanation
$$s = ut - \dfrac {1}{2} gt^2$$
For reaching the ground again, $$ s = 0$$
$$\Rightarrow ut - \dfrac {1}{2} gt^2 = 0$$
$$\Rightarrow t = \dfrac {2u}{g}$$
$$\Rightarrow t \propto u $$ since $$g$$ is constant.
(1) In uniform circular motion, tangential acceleration is zero.
(2) In uniform circular motion, velocity is constant.
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Both 1 and 2 are true and 2 is correct explanation of 1
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Both 1 and 2 are true and 2 is not correct explanation of 1
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1 is true and 2 is false
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1 is false and 2 is true
Explanation
In uniform circular motion tangential acceleration is zero because angular velocity of motion is constant.
And the speed is uniform. But velocity of the particle in uniform circular motion keeps on changing.
Unit of acceleration is
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$$m/s$$
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$$ms$$
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$$m/s^2$$
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none of these
Explanation
acceleration $$ = \dfrac{dv}{dt}$$
Units of 'v' is m/s and 't' is seconds
Therefore units of acceleration is $$\dfrac{m}{s^2} $$
A body moving along a circular path will have :
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a constant speed
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a constant velocity
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no tangential velocity
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a radial acceleration
Explanation
Velocity is not constant since the direction of the ball changes every instance.
The ball has radial acceleration since there is a centripetal force acting on it towards the center.
Ball moving in a circular path has tangential velocity. Cutting the thread , the ball moves tangentially
A vehicle is moving on a road. Ink drops are falling, one at a time, on the road from the vehicle. After the vehicle has moved away, what one observes is shown (qualitatively) in the figure given below. From the figure we can conclude about the vehicle to be moving...
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From left to right with increasing speed
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From left to right with decreasing speed
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From right to left with increasing speed
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From right to left with decreasing speed
Explanation
As we can see the curved surface is towards the left side so the vehicle is moving from left to right and the distance between drops decreases continuously so the speed of the vehicle decreasing.
A body dropped from a height reaches the ground in $$5\;s$$. The velocity with which it reaches the ground is ($$g=9.8\; ms^{-2}$$):
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$$0 \;ms^{-1}$$
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$$49 \;ms^{-1}$$
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$$4.9 \;ms^{-1}$$
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$$9.8 \;ms^{-1}$$
Explanation
$$v = u + gt$$
$$t = 5\ sec$$
$$u = 0$$
$$|v| = 5g = 5 \times 9.8 = 49\ m/s$$
Physical quantity corresponding to the rate of change of displacement is
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Speed
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Velocity
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Acceleration
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Retardation
Explanation
Velocity is the rate of change of displacement
Distance travelled by a freely falling body is proportional to
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Mass of the body
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Square of the acceleration due to gravity
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Square of the time of fall
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Time of fall
Explanation
From the equations of motion
$$ s = ut +\dfrac{1}{2} at^2 $$
$$a=g$$
Assume $$u= 0$$
$$s = \dfrac{1}{2} gt^2$$
From the above equation it is clear that distance travelled is directly proportional to $$ t^2$$
If the velocity of a body does not change, its acceleration is
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Zero
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Infinite
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Unity
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None of these
Explanation
Acceleration of a body is defined as the rate of change of the velocity of the body. Now since the velocity doesn't change at all, the rate of change will be zero.
So, acceleration = 0
Unit for the rate of change of velocity is
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m / s
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$$m / s^2$$
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N s
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N / s
Explanation
Velocity units $$ = m/s$$
Acceleration is the rate of change of velocity
a $$= \dfrac{change \ in \ velocity }{time } $$
Therefore SI units of acceleration is $$ms^{-1}/s = \dfrac{m}{s^2} $$
The displacement of a body which starts from rest, and moving with an acceleration of $$1\ ms^{-2}$$ at the end of $$5\ s$$ in m is:
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12.5
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25
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7.5
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15
Explanation
Using the equations of motion
$$ s = ut + \frac{1}{2} at^2$$
$$u = 0$$ since the body starts from rest
$$ a = 1 m/s^2 $$ and time $$ t = 5s$$
$$s = \frac{1}{2} \times 5^2 $$
$$s = 12.5 m $$
Velocity of a body at rest is always
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Unity
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Negative
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Zero
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Infinite
Explanation
When a body is at rest , the displacement is zero
$$v = \dfrac{s}{t} $$ (s is zero)
Therefore $$v = \dfrac{0}{t} $$
$$v = 0 $$
A body initially moving with a velocity of $$5\ ms^{-1}$$ attains a velocity of $$25\ ms^{-1}$$ in $$5\ s$$, find the acceleration of body in $$ms^{-2}.$$
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$$8ms^{-2}$$
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$$7ms^{-2}$$
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$$4ms^{-2}$$
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$$3ms^{-2}$$
Explanation
Acceleration $$ = \dfrac{\text{Final velocity - initial velocity}}{\text{time taken}}$$
Final velocity $$v = 25 m/s $$
Initial velocity $$u = 5 m/s $$
a $$= \dfrac{25 - 5}{5} m/s^2$$
a $$= 4 m/s^2 $$
A ball is thrown vertically upwards with a speed of $$30\ ms^{-1}$$. The equation for velocity is (Take g= $$10\ ms^{-2}$$)
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$$v=30 + 10t$$
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$$v=30 - 10t$$
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$$v= -10t$$
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$$v= 10t$$
Explanation
$$u=30ms^{-1} ; g=-10ms^{-2}$$
$$v=u+gt$$
$$v=30-10t $$ (As g acting downward so g$$=-10ms^{-2})$$
hence,option B is correct.
The velocity of a body can change
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if its acceleration is zero.
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if its acceleration is non-zero.
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Both A & B
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None of the above.
Explanation
Acceleration is defined as change of velocity in unit time. So if acceleration is zero, there is no change of velocity, the body is moving with a constant velocity.
A body dropped from the top of a tower reaches the ground in 4 s. Height of the tower is :
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39.2 m
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44.1 m
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58.8 m
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78.4 m
Explanation
$$t_d = 4s$$
$$h= \displaystyle \frac{1}{2} g t_d^2 = \frac{1}{2} \times 9.8 \times 4^2$$
$$=4.9 \times 16 = 78.4 m$$
If two masses $$ m_1,\ m_2$$ are thrown vertically upwords with the same velocity, what is the difference in the maximum height gained by them? ($$ m_1 > m_2$$)
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$$m_1$$
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$$m_2$$
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Both reach same height
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None of the above
Explanation
Height is given by,
$$h = ut - (1/2) gt^2$$
Since they are thrown with the same velocity, they will reach the same height.
The expression for the velocity when a body dropped from a height reaches the ground is
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$$V^2 =2s$$
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$$V^2=2gs$$
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$$V=2gs$$
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$$V^2=\frac{gs}{2}$$
Explanation
When a body is dropped from a height h its initial velocity u is zero. Let the final velocity on reaching the ground be V.
From the formula,
$$V^2=U^2+2gs$$, here u=0
$$V^2=2gs$$
Answer (B)
$$V^2=2gs$$
Which of the following is/are true about retardation
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When velocity of a body decreases over time, the rate of change of velocity is known as retardation.
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Its SI unit is $$m/s^2$$.
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It is the negative of acceleration
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All the above.
Explanation
Retardation is opposite of acceleration. In case of acceleration, velocity increases with time and in case of retardation, velocity decreases over time.
The accelerated motion of a body can occur :
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Due to change in its speed only.
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Due to change in direction of motion only.
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Due to change in both speed and direction of motion.
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Due to constancy of velocity.
Explanation
The accelerated motion of a body can occur due to a change in its speed only, due to change in direction of motion only, and due to change in both speed and direction of motion. In the uniform circular motion, the direction of speed changes continuously though the speed is constant, still, the motion is accelerated.
Is it possible to have an accelerated motion with a constant speed? Name such type of motion.
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Yes, Uniform Circular Motion.
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Yes, Non-Uniform Circular Motion.
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Yes, Uniform Linear Motion
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No
Explanation
Yes it is possible. Let us take an example, circular motion. In this it has acceleration because direction of motion is changing but it has constant speed along tangential. Hence it is possible.
Which of the following is/are true about acceleration
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Acceleration is defined as the rate of change of velocity.
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Its SI unit is $$m/s^2$$.
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Negative acceleration is called retardation
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All the above.
Explanation
Acceleration =$$\dfrac{Final\ velocity\ - Initial\ velocity }{time}$$
Its SI unit is =$$ms^{-1}/s=m/s^2$$
A negative acceleration acts opposite to the direction of motion of object and it reduces the velocity , it called retardation.
Which of the following quantity remains constant in a uniform circular motion?
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velocity
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speed
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acceleration
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both velocity and speed
Explanation
In a uniform circular motion, the direction of velocity changes but its magnitude remains constant, hence, speed remains constant in a uniform circular motion.
Hence the correct answer is B
Define velocity. State its unit.
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Velocity is defined as the rate of change of distance of a body with respect to time. Its unit in SI is $$km/s$$.
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Velocity is defined as the rate of change of displacement of a body with respect to time. Its unit in SI is $$km/s$$.
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Velocity is defined as the rate of change of distance of a body with respect to time. Its unit in SI is $$m/s$$.
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Velocity is defined as the rate of change of displacement of a body with respect to time. Its unit in SI is $$m/s$$.
Explanation
Velocity is a vector quantity that refers to the rate at which an object changes its position. It is a vector expression of the displacement that an object or particle undergoes with respect to time.
The SI unit of velocity is meter/second.
Which of the quantities, speed or velocity gives the direction of motion of body ?
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speed
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acceleration
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velocity
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all of the above
Explanation
velocity, a vector quantity, depends on both the body's speed and its direction of travel.
The distance $$x$$ covered in time $$t$$ by a body having initial velocity $${ v }_{ 0 }$$ and having constant acceleration $$a$$ is given by $$x={ v }_{ 0 }t+1/2a{ t }^{ 2 }$$. This result follows from :
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newton's Ist law
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newton's IInd law
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newton's IIIrd law
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none of the above
Explanation
The given equation is the fundamental equation of kinematics. So it can not follow from any Newton's law of motion.
Ans:(D)
A food packet is released from a helicopter rising steadily at the speed of $$2\ { m }/{ s }$$. After $$2$$ seconds the velocity of the packet is (Take $$g=10 { m }/{ { s }^{ 2 } } $$):
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$$22\ { m }/{ s }$$
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$$20\ { m }/{ s }$$
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$$18\ { m }/{ s }$$
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None of these
Explanation
The food packet has an initial velocity $$u= 2\ { m }/{ s }$$ in upward direction,
$$g= 10 \ m/s^2$$
$$t= 2 \ s$$
Using the first equation of motion, $$v = u+at$$
Taking the upward direction as negative and downward direction as positive
$$v=-2+10\times 2=18\ { m }/{ s }$$
Hence, the velocity of the packet is $$18 \ m/s$$ in the downward direction.
What can you say about the motion of an object if its speed-time graph is a straight line parallel to the time axis?
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Object is moving with uniform acceleration
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Object is moving with uniform speed
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Object is moving at rest
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None
Explanation
The correct answer is option (B).
$$\bullet$$
$$\bullet$$ If the speed-time graph is a straight line parallel to the time axis it means that on changing time speed remains constant.
The correct answer is an option (B).
Which of the following is true about distance and time.
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distance and time are always directly proportional to each other.
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distance and time are always indirectly proportional to each other.
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distance and time are directly proportional when the velocity is constant.
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distance and time are indirectly proportional when the velocity is constant.
Explanation
$$ Speed = \dfrac{Distance}{Time} $$
For uniform velocity, Distance $$\propto$$ Time
A body starts from rest and acquires a velocity $$10m s^{-1}$$ in 2 s. Find the acceleration.
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$$10 m s^{-2}$$
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$$20 m s^{-2}$$
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$$5 m s^{-2}$$
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$$40 m s^{-2}$$
Explanation
Acceleration = Change in velocity per unit time.
Therefore, Acceleration $$a = \dfrac{10 m/s}{2 s} = 5 m/s^2 $$
A car starting from rest acquires a velocity $$180\ m s^{-1}$$ in 0.05 h. Find the acceleration.
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$$3600 m s ^{-2}$$
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$$9 m s ^{-2}$$
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$$2 m s ^{-2}$$
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$$1 m s ^{-2}$$
Explanation
Acceleration, $$a = \dfrac{180 m/s}{0.05\times 3600 s} = 1 m/s^2 $$
Name a physical quantity that remains constant in a uniform circular motion.
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Velocity
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Acceleration
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Momentum
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Angular speed
Explanation
As an object moves around in a circle at constant speed (uniform circular motion), both the velocity and the acceleration change. The magnitudes of the velocity and acceleration don't change, but since velocity and acceleration are vectors, the fact that their directions change means that they change.
Momentum is directly proportional to the velocity of the body and hence it changes.
In the uniform circular motion, the angular speed is same for all the particles,
When speed is stated along with its direction, it is called as
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velocity
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acceleration
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jerk
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none of these
Explanation
Velocity of a body is the speed of the body defined along with the direction.
The unit of retardation is
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$$m s^{-1}$$
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$$m s^{-2}$$
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$$m$$
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$$m s^{2}$$
Explanation
Unit of retardation is same as the unit of acceleration i.e. $$m/s^2$$.
When an object is accelerated:
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its direction must be constant
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its velocity is necessarily changing
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its velocity is constant
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its speed is necessarily changing
Explanation
Acceleration is the time rate of change of velocity.
State whether given statement is True or False.
Velocity and speed are measured in different units.
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True
0%
False
Explanation
Velocity and speed have the same dimensions ($$M^0L^1T^{-1}$$) and hence the same unit i.e $$m/s$$
State whether given statement is True or False.
Acceleration is defined as the rate of change of velocity.
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True
0%
False
Explanation
Acceleration
is the rate of change of velocity with time. It is often used to describe a state of increasing speed.
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