CBSE Questions for Class 11 Engineering Physics Laws Of Motion Quiz 3 - MCQExams.com

A body of mass m is rotated at uniform speed along a vertical circle with the help of light string. If $$T_{1} and \ T_{2}$$ are tensions in the string when the body is crossing highest and lowest point of the vertical circle respectively, then which of the following expressions is correct?
  • $$T_{2}-T_{1}=6mg$$
  • $$T_{2}-T_{1}=4mg$$
  • $$T_{2}-T_{1}=2mg$$
  • $$T_{2}-T_{1}=mg$$
A body is moving in a vertical circle such that the velocities of body at different points are critical. The ratio of velocities of body at angular displacements $$60^{0}$$ and $$120^{0}$$ from the lowest point is:
  • $$\sqrt{5}:\sqrt{2}$$
  • $$\sqrt{3}:\sqrt{2}$$
  • $$\sqrt{3}:1$$
  • $$\sqrt{2}:1$$
A ball of mass 0.6kg attached to a light inextensible string rotates in a vertical circle of radius 0.75m such that it has speed of 5 m/s when the string is horizontal. Tension in string when it is horizontal on other side is:
$$(g=10ms^{-2})$$
  • $$30N$$
  • $$26N$$
  • $$20N$$
  • $$6N$$
A simple pendulum is oscillating with an angular amplitude $$60^{0}$$ . If mass of bob is $$50\ g$$, the tension in the string at mean position is:
Consider: $$g=10ms^{-2}$$, length of the string, $$L = 1\ m$$.
  • $$0.5\ N$$
  • $$1\ N$$
  • $$1.5\ N$$
  • $$2\ N$$
Regarding linear momentum of a body
a. It is a measure of quantity of motion contained by the body
b. Change in momentum is the measure of impulse
c. Impulse and acceleration act in opposite direction to the change in momentum
d. In the case of uniform circular motion the linear momentum is conserved.
  • a & b are true
  • b & c are true
  • c & d are true
  • a, b & c are ture
A ball of mass 'm' is projected from the ground with a speed 'u' at an angle ' $$\alpha $$' with the horizontal. The magnitude of the change in momentum of the ball over a time interval from begining till it strikes the ground again is
  • $$\dfrac {mu\sin{ \alpha } }{ 2 } $$
  • $$2mu\cos { \alpha } $$
  • $$\dfrac { mu{ \cos { \alpha } } }{ 2 } $$
  • $$2mu \sin { \alpha } $$
A water bucket of mass '$$m$$' is revolved in a vertical circle with the help of a rope of length '$$r$$'. If the velocity of the bucket at the lowest point is $$\sqrt{7gr}$$ . Then the velocity and tension in the rope at the highest point are:
  • $$\sqrt{3gr},2mg$$
  • $$\sqrt{2gr},mg$$
  • $$\sqrt{gr},mg$$
  • $$Zero$$ , $$Zero$$
A person carries a hammer on his shoulder and holds the other end of its light handle in his hand. Let $$y$$ be the distance between his hand and the point of support. If the person changes $$y$$, the pressure on his hand will be proportional to:
  • $$y$$
  • $$y^{2}$$
  • $$\dfrac{1}{y}$$
  • $$\dfrac{1}{y^{2}}$$
An impulse is supplied to a moving object with the force at an angle of $$120^{0}$$ with the velocity vector. The angle between the impulse vector and the change in momentum vector is
  • $$120^{0}$$
  • $$0^{0}$$
  • $$60^{0}$$
  • $$240^{0}$$
A pilot of mass $$m$$ can bear a maximum apparent weight $$7$$ times of $$mg$$. The aeroplane is moving in a vertical circle. If the velocity of aeroplane is $$210\ m/s$$ while driving up from the lowest point of vertical circle, the minimum radius of vertical circle should be:
  • $$375\ m$$
  • $$420\ m$$
  • $$750\ m$$
  • $$840\ m$$
A body of mass $$2\ kg$$ attached at one end of light string is rotated along a vertical circle of radius $$2\ m$$. If the string can withstand a maximum tension of $$140.6\ N$$, the maximum speed with which the stone can be rotated is:
  • $$22\ m/s$$
  • $$44\ m/s$$
  • $$33\ m/s$$
  • $$11\ m/s$$
A body is revolving in a vertical circle of radius r such that the sum of its $$K.E.$$ and $$P.E.$$ is constant. If the speed of the body at the highest point is $$\sqrt{2gr}$$ then the speed of the body at the lowest point will be:
  • $$\sqrt{7gr}$$
  • $$\sqrt{6gr}$$
  • $$\sqrt{8gr}$$
  • $$\sqrt{9gr}$$
A vehicle is travelling with uniform speed along concave road and then along convex road of same radius of curvature. If the normal reaction on the vehicle is half of its weight as it reaches highest point of convex road, then normal reaction on the vehicle as it reaches lowest point of concave road is:
  • twice weight of vehicle
  • thrice weight of vehicle
  • $$1.5$$ times weight of vehicle
  • $$\sqrt{2}$$ times weight of vehicle
A vehicle is travelling at uniform speed $$36\ kmph$$ along a fly-over bridge and a person of mass $$50\ kg$$ in the vehicle experiences a normal reaction $$390\ N$$ as the vehicle crosses the highest point. The radius of curvature of the fly-over bridge is:
  • $$40\ m$$
  • $$50\ m$$
  • $$80\ m$$
  • $$100\ m$$
The bob of a simple pendulum at rest position is given a velocity $$V$$ in horizontal direction so that the bob describes vertical circle of radius equal to length of pendulum $$l$$ . If the tension in string is $$4$$ times weight of bob when the string is horizontal, the velocity of bob when it is crossing highest point of vertical circle is:
  • $$\sqrt{\dfrac{gl}{2}}$$
  • $$\sqrt{gl}$$
  • $$\sqrt{\dfrac{3gl}{2}}$$
  • $$\sqrt{2gl}$$
A simple pendulum is oscillating with an angular amplitude $$60^{0}$$. If mass of bob is $$50\ gram$$, the tension in the string at mean position is:
$$(g=10\ m/s^{2})$$
  • $$0.5\ N$$
  • $$1\ N$$
  • $$1.5\ N$$
  • $$2\ N$$
An army vehicle is travelling at uniform speed along convex road then along concave road of same radius of curvature and finally along horizontal road. $$R_{1},R_{2}$$ and $$R_{3}$$  are normal reactions on the vehicle while crossing highest point of convex road, lowest point of concave road and horizontal road respectively. Which of the following relation is true?
  • $$R_{1}< R_{2}< R_{3}$$
  • $$R_{1} > R_{2} > R_{3}$$
  • $$R_{2} > R_{3} > R_{1}$$
  • $$R_{2}=\dfrac{R_{1}+R_{3}}{2}$$
A particle starts sliding down from the top of the smooth convex hemisphere of radius $$30$$$$cm$$, placed horizontally with convex side up. The vertical distance at which particle leaves the surface from it's highest point is:

20045_7da7cc49c1264d678ac5ca9ab3535738.png
  • $$5$$$$cm$$
  • $$10$$$$cm$$
  • $$15$$$$cm$$
  • $$20$$$$cm$$
The bob of a simple pendulum of mass $$'m'$$ is performing oscillations such that the tension in the string is equal to twice the weight of the bob while it is crossing the mean position. The tension in the string when the bob reaches extreme position is :
  • $$\dfrac{mg}{2}$$
  • $$mg$$
  • $$\dfrac{3mg}{2}$$
  • zero
A simple pendulum consists of a light string from which a spherical bob of mass, $$M$$, is suspended. The distance between the point of suspension and the center of bob is $$L$$. At the lowest position, the bob is given tangential velocity of $$\sqrt{5gL}$$. The K.E of the bob when the string becomes horizontal is:
  • $$0$$
  • $$\dfrac{MgL}{2}$$
  • $$\dfrac{3MgL}{2}$$
  • $$\dfrac{5MgL}{2}$$
The bob of a simple pendulum is given a velocity in horizontal direction when the bob is at lowest position ,so that the bob describes vertical circle of radius equal to length of pendulum and tension in the string is $$10 \ N$$ when the bob is at an angle $$60^0$$ from lowest position of vertical circle. The tension in the string when the bob reaches highest position is (The mass of bob is $$ 100$$ gram. $$g = 10\ ms^{–2}$$):
  • $$9\  N$$
  • $$7 \ N$$
  • $$5.5\  N$$
  • $$3.5 \ N$$
A small block is freely sliding down from the top of a rough inclined plane whose angle of inclination is $$45^{0}$$. The block reaches bottom then it completes a smooth vertical circle. If the coefficient of friction is $$0.5$$, the ratio of minimum vertical height of inclined plane to radius of vertical circle is:
  • $$3:1$$
  • $$5:1$$
  • $$5:2$$
  • $$7:3$$
A simple pendulum is oscillating with an angular amplitude $$60^o$$. If $$m$$ is mass of bob and $$T_1$$, $$T_2$$ are tensions in the string, when the bob is at extreme position, mean position respectively then is:

A) $$T_1 = \dfrac{mg}{2}$$
B) $$T_2 = 2\ mg$$
C) $$T_1 = 0$$
D) $$T_2 = 3\ mg$$
  • A and B are true.
  • A and D are true.
  • B and C are true.
  • C and D are true.
The length of a simple pendulum is  '$$L$$'. Its bob from rest position is projected horizontally with a velocity $$\sqrt{\dfrac{7gL}{2}}$$. The maximum angular displacement of bob, such that the string does not slack, is:
  • $$30^o$$
  • $$60^o$$
  • $$120^o$$
  • $$150^o$$
The length of a ballistic pendulum is $$1 m$$ and mass of its block is $$1.9 kg$$. A bullet of mass $$0.1 kg$$ strikes the block of ballistic pendulum in horizontal direction with a velocity $$100ms^{–1}$$ and got embedded in the block. After collision the combined mass (block & bullet) swings away from lowest point. The tension in the string when it makes an angle $$60°$$ with vertical is  $$(g=10ms^{-2})$$:
  • $$20\  N$$
  • $$30\  N$$
  • $$40\  N$$
  • $$50\  N$$
A small mass lying at the top of a smooth convex hemisphere is just pushed horizontally. The angle with the vertical where it looses contact with surface is:
  • $$tan^{-1}(\dfrac{2}{3})$$
  • $$sin^{-1}(\dfrac{2}{3})$$
  • $$cos^{-1}(\dfrac{2}{3})$$
  • $$cot^{-1}(\dfrac{2}{3})$$
A car is travelling with uniform speed on a flyover bridge which is a part of vertical circle whose radius of curvature is $$60\ m$$. A person in that car feels $$75\%$$ decrease in his weight when the car is crossing highest position. The speed of car at that position is:
  • $$28\ m/s$$
  • $$21\ m/s$$
  • $$14\ m/s$$
  • $$7\ m/s$$
A simple pendulum of length $$50 cm$$ is suspended from a fixed point $$O$$ and a nail is fixed at a point $$P$$ which is vertically below $$O$$ at some distance. The bob is released when string is horizontal. The bob reaches lowest position then it describes vertical circle whose centre coincides with point $$P$$. The minimum distance between $$O$$ and $$P$$ is:
  • 20 cm
  • 25 cm
  • 30 cm
  • 40 cm
Mass of the bob of a simple pendulum of length $$L$$ is $$m$$. If the bob is projected horizontally from its mean position with velocity $$\sqrt{4gL}$$ , then the tension in the string becomes zero after a vertical displacement of :
  • $$L/3$$
  • $$3L/4$$
  • $$4L/3$$
  • $$5L/3$$
Two bodies A, B of masses $$m_1, m_2$$ are knotted to a mass-less string at different points rotated along concentric circles in horizontal plane. The distances of A, B from common centre are 50cm, 1m. If the tensions in the string between centre to A and A to B are in the ratio 5:4, then the ratio of $$m_{1}$$ to $$m_{2}$$ is:
  • 2 : 3
  • 3 : 2
  • 1 : 1
  • 1 : 2
A curved road is $$7.5\ m$$ wide and its outer edge is raised by $$1.5\ m$$ over the inner edge. The radius of curvature is $$50\ m$$. For what speed of the car is this road suited?$$(g=10m/s^{2})$$:
  • $$5\ m/s$$
  • $$10\ m/s$$
  • $$15\ m/s$$
  • $$20\ m/s$$
A block of mass m is in contact with the cart as shown in figure

The coefficient of static friction between the block and the cart is . The acceleration of the cart that will prevent the block from falling satisfies
68585.jpg
  • $$\alpha > \frac{mg}{\mu }$$
  • $$\alpha > \frac{g}{\mu m}$$
  • $$\alpha \geq \frac{g}{\mu }$$
  • $$\alpha < \frac{g}{\mu }$$
STATEMENT-1
It is easier to pull a heavy object than to push it on a level ground.
STATEMENT-2
The magnitude of frictional force depends on the nature of the two surfaces in contact.
  • STATEMENT-1 is True, STATEMENT-2 is True; STATEMENT-2 is a correct explanation for STATEMENT-1
  • STATEMENT-1 is True, STATEMENT-2 is True; STATEMENT-2 is NOT a correct explanation for STATEMENT-1
  • STATEMENT -1 is True, STATEMENT-2 is False
  • STATEMENT -1 is False, STATEMENT-2 is True
Instantaneous power of constant force acting on a particle moving in a straight line under the action of this force 
  • is constant
  • increases linearly with time
  • decreases linearly with time
  • either increases or decreases linearly with time
A block is freely starts sliding down on a rough inclined plane from a vertical height $$5\  m$$. The block reaches the bottom of inclined plane then it just describes vertical circle of radius $$1.2\  m$$ along smooth track. The percentage of energy wasted due to friction is:
  • $$20$$ %
  • $$30$$ %
  • $$40$$ %
  • $$60$$ %
In the following figure all surfaces are assumed to be frictionless and pulley is assumed to be ideal. The block 'A' is projected towards the pulley 'P' with an initial velocity $$u_0$$ then select incorrect option


72571.jpg
  • the string would become tight at $$t=\dfrac{2u_0}{g}$$
  • the distance travelled by 'A' before the string is taut is $$\dfrac{u_0^2}{g}$$
  • the distance travelled by 'B' before string is taut is $$\dfrac{2u_0^2}{g}$$
  • the common speed of the blocks just after the string is taut is $$\left [ \dfrac{n+2}{n+1} \right ]u_0$$
A body is moving in a vertical circle of radius '$$r$$' by a string. If the ratio of maximum to minimum speeds is $$\sqrt{3}:1$$ , the ratio of maximum to minimum tensions in the string is:
  • 3 : 1
  • 5 : 1
  • 7 : 1
  • 9 : 1
A block of mass $$m$$ is freely sliding down on a smooth inclined plane from its top. The block reaches the bottom of inclined plane and then describes a vertical circle of radius $$r$$ along smooth track. If vertical height of inclined plane is $$3r$$, the normal reaction on the block when it is crossing highest point of vertical circle:
  • $$2mg$$
  • $$mg$$
  • $$\dfrac{mg}{2}$$
  • $$Zero$$
A horse continues to apply a force in order to move a cart with a constant
speed. This is because:
  • the force applied by the horse balances the gravitational force.
  • the force applied by the horse balances the force of friction.
  • Horse does not apply any force.
  • None of these
A mass $$0.1\ kg$$ is rotated in a vertical circle using the cord of length $$1\ m$$, when the cord makes an angle $$60^0$$ with the vertical, the speed of the mass is $$3\  m/s$$ the resultant  radial acceleration of mass in that position is:
  • $$9m/s^{2}$$
  • $$4.9m/s^{2}$$
  • $$4.1m/s^{2}$$
  • zero
A tennis ball and an iron ball is thrown towards us with the same velocity. Then, the tennis ball is easy to catch as compared to an iron ball.
  • True
  • False
A system of $$n$$ particles is free from any external force. Which of the following is true for the magnitude of the total momentum of the system?
  • It must be zero
  • It could be non-zero, but it must be constant
  • It could be non-zero, and it might not be constant
  • The answer depends on the nature of the internal forces in the system
S.I. unit of momentum is :
  • $$kg\ ms^{-1}$$
  • $$kg\ mg^{-2}$$
  • $$kg\ mg^2$$
  • $$kg\ m^{-1}s^{-1}$$
A rubber ball of mass 250 g hits a wall normally with a velocity  $$10 m s^{-1}$$ and bounces back with a velocity of $$8 m s^{-1}$$. The impluse is _______N s.
  • $$-0.5$$
  • $$+0.5$$
  • $$-4.5$$
  • $$+4.5$$
A force of 10 N acts on a body for 3 microsecond $$(\mu s)$$. Calculate the impulse. If mass of the body is 5 g, calculate the change of velocity.
  • $$6 \times 10^{-3} m s^{-1}$$
  • $$3 \times 10^{-3} m s^{-1}$$
  • $$8 \times 10^{-3} m s^{-1}$$
  • $$16 \times 10^{-3} m s^{-1}$$
The increase in base area leads to decrease in stability of an object.
  • True
  • False
..... of Roads is done by raising the outer edges of the road slightly above the level of inner edge, to avoid accidents.
  • Finishing
  • Banking
  • Inclination
  • None of these
A stone of mass $$1 kg$$ tied to a light inextensible string of length $$L=\dfrac{10}{3}m$$ is whirling in a circular path of radius $$L$$ in a vertical plane. If the ratio of the maximum tension in the string to the minimum is $$4$$ and if $$g$$ is taken to be $$10 \ m/s^2$$, then speed of stone at the highest point of the circle is
  • $$20 m/sec$$
  • $$10\sqrt{3}  \ m/sec$$
  • $$5\sqrt{2}  \ m/sec$$
  • $$10 m/sec$$
China wares are wrapped in straw or paper before packing. This is the application of concept of :
  • Impulse
  • Momentum
  • Acceleration
  • Force
A particle of mass $$m$$ is projected with a velocity $$6\hat { i } +8\hat { j } $$. Then the magnitude of change in momentum when it just touches ground will be
  • $$0$$
  • $$12m$$
  • $$16m$$
  • $$20m$$
0:0:1


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