Motion And Time - Class 7 Physics - Extra Questions

What are uniform and non-uniform motions?

 Uniform Motion Non uniform motion
 A body is said to be in uniform motion if it covers equal distances in equal intervals of time. A body is said to be in non uniform motion if it covers unequal distances in equal intervals of time.


Observe the following motions and classify them as uniform motion,non-uniform motion and circular motion. 
(1) Motion of a football player, 
(2) Motion of a fan,
(3) Motion of an ant, 
(4) Motion of a town bus, 
(5) Motion of the moon, 
(6) Motion of spectators in an auditorium, 
(7) Motion of the arms of clock.

A body is said to be in uniform motion if it covers equal distances in equal intervals of time, and in non-uniform motion, if it covers unequal distances in equal intervals of time.

When a body is moving in a circular path about a fixed point, it is said to be in a circular motion.

i) A football player does not cover equal distances in equal time intervals, so it's a non-uniform motion.
ii) Fan rotates about the axis it is hanging with, so it's a circular motion. It is also an example of uniform motion as it moves with a constant speed at a particular time.
iii) Motion of an ant is a non-uniform motion.
iv) A town bus does not cover equal distances in equal time intervals, it is non-uniform motion.
v) Moon revolves around the earth and covers equal distances in equal time intervals, it is uniform and circular motion.
vi) Motion of spectators in an auditorium is an example of non-uniform motion.
vii) Motion of arms of a clock is circular and uniform motion.


A person travels a distance of $$72 \ km$$ in $$4$$ hours. Calculate speed in $$m/s$$.

Distance, $$S=72\ km$$
Time, $$t=4 \ hr$$
Speed $$=\dfrac{72}{4}km/hr\\ = \dfrac{72}{4}\times \dfrac{5}{18}\\=5 \ m/s$$


A body at rest cannot have ______ and ______.

A body at rest can not have speed and velocity because distance and displacement do not change with time.
Answer: velocity and speed


Can the speed of a body be negative?

No, speed of a body can never be negative.
speed  = $$\dfrac{Distance}{time}$$
As neither time nor distance covered by a body can be negative, therefore, speed also cannot be negative.


The distance between two stations is $$240$$km. A train takes $$4$$ hours to cover this distance. Calculate the speed of the train.

Distance $$=240$$km
Time taken $$=4$$ hours
Speed$$=$$ Distance covered $$/$$time taken $$=240km/4$$ hr
                         $$=60km/h$$
Speed of train $$=60km/h$$.


A train travels at a speed of 180 km/h. How far will it travel in 4 hours?

Speed of train  $$v = 180 \ km/h$$
Time taken   $$t = 4 \ h$$
So, distance cover by train  $$D = vt$$
$$\implies \ D = 180\times 4 = 720 \ km$$


Arun completed a 100-meter race in 16s, while Karthik finished it in 13s. Who ran faster?

Speed of runners  $$v = \dfrac{Distance}{Time  \ taken}$$
Since time taken by Karthik is less than that taken by Arun, thus speed of Karthik is more than that of Arun.
Hence Karthik ran faster.


Name the instrument which measures the distance covered by a vehicle. 

An $$\mathbf{Odometer}$$ or odograph is an instrument used for measuring the distance travelled by a vehicle, such as a bicycle or car. 


A man covers $$36$$ km in $$1$$ hour. Find his speed in meters/second.

We know that $$speed=\dfrac{distance}{time}$$

Given that the distance covered by a man is $$36km=36\times 1000m$$

Given that the time required to cover is $$1hour=60\times 60sec$$

Therefore, $$speed=\dfrac{36\times 1000}{60\times 60}=10m/sec$$


Change the speed of $$6\ m/s$$ into $$km/h$$

Given that,

Speed $$v=6\,m/s$$

Now, speed in $$km/h$$

  $$ v=6\times \dfrac{18}{5} $$

 $$ v=21.6\,km/h $$

Hence, the speed is $$21.6\ km/h$$



A man walks on a straight road from his home to a market 3 Km away with a speed of 6 Km/h. The time taken by the man to go from his home to market equals

Given,

Distance, $$D=3\,km$$

Speed, $$V=6\,km{{h}^{-1}}$$

Time = Distance/ speed

$$t=\dfrac{D}{V}=\dfrac{3\,}{6}=0.5\,hr=30\,\min $$

Hence, in 30 min he reaches market from home.



Given two examples of bodies in non-uniform motion.

A body is said to be in non-uniform motion if it covers unequal distances in equal intervals of time. For example:
(i) Free falling stone
(ii) Car moving with a constant acceleration


Name the physical quantity obtained by dividing 'Distance travelled' by Time taken' to travel that distance.

Speed is unit that is defined as the distance traveled per unit time. 


Write a brief note on uniform and non-uniform motion.

Uniform MotionNon-uniform Motion
If the motion of a body has zero acceleration, then the motion is called uniform motionIf the motion of a boxy has non-zero acceleration, then the motion is called non-uniform motion
In uniform motion body moves with a constant speed and in same directionIn a non-uniform motion, either speed or direction or both changes
Average speed $$=$$ Instantaneous speedAverage Speed $$\ne$$ Instantaneous speed


Define speed?

Speed is a way of measuring how quickly something is moving or being done, or something moving fast. An example of speed is a car being driven $$45$$ miles per hour. An example of speed is someone cleaning a room in $$10$$ minutes.   


Bus X travels a distance of 360 km in 5 hours whereas bus Y travels a distance of 476 km in 7 hours. Which bus travels faster ? 

For bus X. 
Speed = $$\dfrac{Distance}{Time}$$
Speed=$$\dfrac{360}{5}=72\ km/h$$ 

For bus y, 
Speed = $$\dfrac{Distance}{Time}$$
Speed=$$\dfrac{476}{7}=68\ km/h$$

Speed of bus X is more than that of bus Y. 
Hence, bus X travels faster. 


Arrange the following speeds in increasing order (keeping the least speed first): 
An athlete running with a speed of  $$10 \,m/s$$.
A bicycle moving with a speed of $$200 \,m/min$$.
A scooter moving with a speed of $$30\, km/h$$. 

Speed of athelete $$ = 10\ m/s$$ 

Speed of bicycle $$= 200\, m/min = 200/60 m/s = 3.33 \,m/s$$ 

Speed of scooter $$= 30 \,km/h = 30000/3600\, m/s = 8.33\ m/s$$

$$ 3.33 m/s < 8.33 \, m/s < 10 \, m/s $$

i.e. $$200\, m/min < 30 \,km/h < 10\, m/s$$ 


Name the physical quantity which gives us an idea of how slow or fast a body is moving.

Speed gives an idea of how slow or fast a body is moving. 


What do the following measure in a car ?
(a) Speedometer
(b) Odometer.

(a) The speedometer of a car measures instantaneous speed of the car. 
(b) Odometer is a device used to record the distance travelled by the car. 


A simple pendulum is oscillating between two points A and B as shown in Fig. 13.5 is the motion of the bob uniform or non-uniform ?
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A simple pendulum is oscillating between two points A and B is uniform motion. As Bob (small metallic ball) moves in a constant speed throughout the motion so it is a uniform motion


If Boojho covers a certain distance in one hour and paheli covers the same distance in two hours, who  travels in a higher speed ?

Let the distance cover by Boojho be x km

So, the speed of Boojho will be =  km/h

Paheli also cover x km, so her speed will be =  km/h

So, we can see that Boojho travels with higher speed higher than Paheli.



Paheli and Boojho have to cover diffrent distance to reach their school but they take the same time to reach the school . What can you say about their speed? 

As Paheli and Boojho both reach school at the same time but their distance to reach school is different so we can say that their speed is different. The one who covers more distance has more speed than those who cover less.



A car travels with a speed $$12 \ m s^{-1}$$, while a scooter travels with a speed $$36 \ km h^{-1}$$. Which of the two travels faster ?

Speed of car = $$ 12 \ m  s^{-1} $$
Speed of scooter = $$ 36 \ km h^{-1} $$

Since, $$ 1 \ km = 1000 \ m$$
and, $$1 \ hr = 3600 \ sec$$

$$ \therefore $$ Speed of scooter =  $$36 \ km/hr = \dfrac{36\times 1000}{3600} \ m/s$$ = $$ 10 \ ms^{-1} $$

Hence, the car travels faster than the scooter.


Give two examples to illustrate that a body can have two or more types of motion simultaneously.

Part 1: Mixed motion

A body which has more than one type of motion associated with it is called Mixed motion. 


Part 2: Examples 

Example :

(i) Motion of earth around the sun is a circular motion, however due to its own rotation  around its axis earth has rotatory motion associated with it too.

(ii) Wheels of train moving along the track have both translational as well rotatory motion associated with it.




Differentiate between periodic and non-periodic motions by giving an example of each.

Periodic Motion

Non - Periodic motion

Any motion which gets repeated after regular intervals of time is called a

periodic motion.


Motion which does not get repeated after regular intervals of time are non periodic motion.

Ex.- Motion of earth around the sun is an example of periodic motion. Since it completes one revolution in 365 days and motion is repeated after every 365 days.

Ex.- The motion of a cricket ball hit by a batter is an example of non periodic motion since the motion of the ball doesn’t get repeated.




Explain the meaning of term speed.

The distance covered by an object per unit time is known as speed.

$$ Speed = \dfrac{Distance}{Time} $$

The SI unit of speed is $$m/s$$.


What do you mean by a mean solar day ?

Mean solar day is the time taken by the earth to make one complete rotation about its own axis.


Name the type/types of motion being performed by each of the following:
Blades of an electric fan in motion.

Circular motion, Periodic motion

Solution:

  • Blades of a fan are in circular motion.

  • This is because the fan is rotating about its own axis, however the blades do not rotate  about an axis passing through them.

  • Instead a point on the blade undergoes revolution about an axis passing through the centre of the fan

A circular motion of fan is also periodic.




Name two devices used to measure the short time interval of an event.

Two devices used to measure the time interval of an event are 
1. StopWatch
2. StopClock


State the types of motion of the following :
The needle of a sewing machine

Answer: Oscillatory motion


Solution:

Explanation

The motion of needle of a sewing machine is to and fro motion about its mean position, so it is an example of oscillatory motion




One to and fro motion of a clock pendulum takes time = ______ .

One to and fro motion of a clock pendulum takes time  =  $$2 s$$.


State the types of motion of the following :
The drill machine

Answer: Mixed = Translational and Rotatory motion


Explanation

A drilling machine is also an example of mixed motion i.e. translational motion combined with rotatory motion. 

This is because when the drill bit of the drilling machine is making a slot, the drill bit is rotating at a very high speed.

Also while making the slot, the drill bit is moving forward further into the slot, thereby performing a translational motion as well.




A boy travels with an average speed of $$10 \ m s^{-1}$$ for $$20 $$ min. How much distance does he travel?

Average speed of boy = $$10 \ m s^{-1}$$
Time taken = $$20 \ min$$ 

Using, Distance travelled = Speed $$\times $$ Time taken

Convert minutes into seconds
$$1$$ minute = $$60$$ sec.
$$20$$ minutes = $$20 \times 60 = 1200 \ sec$$.

Distance travelled $$= 10 \ m s^{-1} \times 1200 \ sec$$ 
.$$= 12000\ m$$  or $$12 \ km$$ 


A car covers a distance of $$160\ km$$ between two cities in $$4\ h$$. What is the average speed of the car?

Given,
$$d = 160\ km$$; distance covered
$$t = 4\ h$$; time is taken between two cities
So, speed 

$$v = \dfrac{Distance}{Time}$$

$$\Rightarrow v = \dfrac{160\ km}{4\ h}$$

$$\Rightarrow v  = 40\ km\ h^{-1}$$


Distinguish between uniform and non-uniform motions, giving an example of each.

Uniform motion

Non uniform motion

Body travels equal distance in equal intervals of time in a straight line.

Body covers unequal distances in equal intervals of time in a straight line.

Direction of motion does not change

Direction of motion may change

Ex.- Motion of a car moving in a straight line with a constant speed.

Ex.- A car moving through the market is an example of non uniform motion as the speed of the car is varying continuously due to traffic.




A car travels a distance of 15 km in 20 minutes. Find the speed of the car in $$ m s^{-1} $$

Speed of car in  $$ m s^{-1} $$
Convert 15 km into meters
1 km = 1000 m
15 km = $$ 1000 \times 15 $$ = 15000 m                   ......(i)
Convert minutes into seconds
1 minutes = 60 sec.
20 minutes = $$ 60 \times 20 $$ = 1200 sec ........ (ii)
Speed of car = $$ \dfrac{distance}{time} $$

Speed of car = $$ \dfrac{15000 m}{1200 sec} $$ = $$ 12.5 m  s^{-1} $$


Define speed. What is its S.I unit?

Speed can be defined as the rate of change of distance with regards to time. The S.I. unit of time is meter per second $$(m/s)$$.


Express $$15\ m/s$$ in $$km/h$$.

We know,
$$1\ km=1000\ m$$

$$1\ m=\dfrac{1}{1000}\ km$$

$$1\ h=60\ min=60\times 60\ s$$
$$1\ h =3600\ s$$

$$1\ s=\dfrac{1}{3600}\ s$$

Therefore,
$$15\ m/s=15\times \dfrac{1/1000}{1/3600}\ km/h$$

$$15\ m/s= \dfrac{15\times 3600}{1000}\ km/h$$

$$15\ m/s= 54\ km/h$$


Arrange the following speeds in increasing order:
$$10\ \text{ms}^{-1}, 1\ \text{km min}^{-1}, 18\ \text{km h}^{-1}$$

In order to arrange the following in increasing order of their speeds, we must first bring them all to a similar unit.
Expressing all the three in $$ms^{-1}$$
$$10\ ms^{-1}$$ is already in $$ms^{-1}$$
$$1\ km\ min^{-1}=1\times 1000/60=16.67\ ms^{-1}$$
$$18\ km\ h^{-1}=\dfrac{18\times 1000\ m}{60\times 60}=5\ ms^{-1}$$
Hence, the increasing order is $$18\ km\ h^{-1}, 10\ ms^{-1}, 1\ km\ min^{-1}$$


What can you say the nature of motion of a body if its displacement-time graph is a straight line parallel to time axis ?

The following can be deduced about the nature of motion of a body, if its displacement-time graph is:
A straight line parallel to time axis- it depicts that the body is at rest because the displacement is not changing with time. Therefore, body is not in motion.
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What are uniform and non-uniform speed?

  1. In an object that covers equal distance in equal intervals of time, it is said to be uniform motion.
  2. Non-uniform motion: If an object covers the unequal distance in equal intervals of time, it is said to be non-uniform motion.


What is a position-time graph?

A graph drawn by taking time along the x-axis and displacement along the y-axis is called a position-time graph.


A car moving on a straight path covers a distance of $$1\ km$$ due to east in $$100\ s$$. What is the speed of the car?

Given,
Distance, $$d=1\ km=1000\ m$$
time taken, $$t=100s$$

$$Speed =\dfrac{distance}{time}$$

$$Speed =\dfrac{1000}{100}=10\ ms^{-1}$$


What does the odometer of an automobile measure?

Odometer, or odograph, is a device that measures the distance travelled by an automobile based on the perimeter of the wheel as the wheel rotates. The odometer gives us only the measure but doesn't show the direction of distance .


Write the formula of speed.

$$ Speed = Distance / Time $$


The speed of a car is $$72\ kmh^{-1}$$. Express it in $$m/s$$.

Given: 
Speed $$=72\ kmhr^{-1}$$
Speed in $$ms^{-1}$$
$$\Rightarrow 72\ kmhr^{-1}=\dfrac{72\times 1000\ m}{60\times 60}$$
$$\Rightarrow \text{speed}=20\ ms^{-1}$$


Give one example of linear motion

Moving of stone falling from a certain height. Linear motion a motion in which particle moves in a state line.


Give two examples for vibrational motion.

The two examples of the Vibrational motion are:
The string of a guitar
Surface of drums


What are the uses of distance time graph?

The uses of distance – time graphs are :
1. The nature of motion is given at a glance.
2. The relative motion at various intervals can.
3. The region of acceleration or retardation can be estimated without any calculation.
4. The distance of moving body at any time unit can be calculated.


A bus travels $$54$$km in $$90$$ minutes. The speed of the bus is (in m/s)?


Step-1 Given data

Step-2 Calculations
Speed $$v=\dfrac{d}{t}
=\dfrac{54000m}{5400sec}=10m/s$$.


Bus A covered 75 m in 5 s. Bus B covered 169 m in 13 s.
Which bus has a higher speed?

We know
Speed $$=\dfrac{distance}{time}$$

Speed of $$A=\dfrac{75}{5}=15\ m/s$$

Speed of $$B=\dfrac{169}{13}=13\ m/s$$
So the bus $$A$$ has higher speed


Distance travelled by the object in unit time is ________ .

speed


Calculate the speed of the body.

Distance $$=AB+BC=60+40=100\ m$$
Time $$=6s+4s=10\ sec$$
$$\therefore$$ Speed $$=\dfrac{Distance}{Time}=\dfrac{100}{10}=10\ m/s$$


Give Reasons for the following:
If the reading on the odometer of a vehicle in the beginning of a trip and after $$40$$ minutes were $$1048km$$ and $$1096km$$ respectively, will the reading on the speedometer show this velocity where the vehicle is moving? Support your answer with reason.

Odometer is used to measure the distance traveled by the vehicle 
Given:
Initial Reading$$=1048km$$ at $$t=0$$ seconds
Final Reading $$=1096km$$ at $$t=40$$ minutes$$=\cfrac{40}{60}hr$$
$$Average\quad speed=\cfrac { Total\quad Distance\quad Covered }{ Total\quad Time\quad Taken } =\cfrac { 1096-1048 }{ 40/60 } =\cfrac { 48 }{ 40/60 } =72km\quad { hr }^{ -1 }$$
Calculations using the readings of odometer gives the average speed
Whereas, the speedometer gives the reading of instantaneous speed.
Thus, the two values, that is one calculated and one on the speedometer may not be the same
Both can only be the same if the vehicle has been moving with constant velocity throughout the measurement.


What does an odometer do?

An odometer is a device that is used for measuring the distance traveled by a vehicle such as motor cycle or car. The odometer is usually situated in the vehicle's dashboard. The word "odometer" is derived from two Greek words meaning path and measure.

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The speed of a bus is 72 km/h, whereas the speed of a car is 125 m/s. Which vehicle moves faster?

Speed of bus   $$v_b = 72 \ km/h$$
$$\therefore$$  $$v_b = 72 \ km/h\times \dfrac{1000 \ m}{km}\times \dfrac{1 \ h}{3600 \ s}$$
$$\implies \ v_b = 20 \ m/s$$
Speed of car  $$v_c = 125 \ m/s$$
Thus car moves faster than bus.


Define speedometer and odometer.

Speedometer is a device in vehicles it records the speed of the vehicle directly in kilometer / hour. Odometer that measures the distance traveled (moved) by the vehicle.


How do you measure the time?

Time can be measured using a simple pendulum or stopwatch. The time measuring instruments exhibit two basic components: (1) a regular, constant, or repetitive action to mark off equal increments of time, and (2) a means of keeping track of the increments of time and of displaying the result.


What natural phenomena could serve as alternative time standards?

The natural phenomena could serve as time standards are:
1. Position of the sun in the day time
2. Position of the moon in the night time
3. Position of stars in the night time
4. Changes of seasons, etc.


Class 7 Physics Extra Questions