# Motion and Time (NCERT Solutions, Class 7)

(1) Classify the following as motion along a straight line, circular or oscillatory motion:

(i)Motion of your hands while running

(ii)Motion of a horse pulling a cart on a straight road

(iii) Motion of a child in a merry- go – round.

(iv) Motion of a child in a see-saw.

(v) Motion of a hammer of an electric bell.

(vi) Motion of a train on a straight bridge.

Ans-

 S.N. Example of motion Type of motion 1. Motion of your hands while running Oscillatory 2. Motion of a horse pulling a cart on a straight road. Straight line 3. Motion of a child in a merry- go – round. Oscillatory, Circular 4. Motion of a child in a see-saw. Oscillatory 5. Motion of a hammer of an electric bell. Oscillatory 6. Motion of a train on a straight bridge. Straight line

(2) Which of the following are not correct?

(i) The basic unit of time is second.

(ii) Every object moves with a constant speed.

(iii) Distances between two cities are measured in kilometers.

(iv) The time period of a given pendulum is not constant.

(v) The speed of a train is expressed in m/s.

Ans – The sentences which are not correct is given below:

(ii) Every object moves with a constant speed.

(iv)The time period of a given pendulum is not constant.

(v) The speed of a train is expressed in m/s.

(7) Show the shape of the distance – time graph for the motion in the following cases:

(i) A car moving with a constant speed.

(ii) A car parked on a side road.

Ans-

(i) The shape of the distance – time graph for a car moving with a constant speed will always be straight line because car travel equal distance in equal interval of time. The graph is shown below:

(ii) The shape of the distance – time graph for a car parked on a road side will always be horizontal straight line parallel to time axis(x axis) because car is not travelling any distance with the increase of time. The graph is shown below:

(9) The basic unit of speed is;

(i) km/min

(ii) m/min

(iii)km/h

(iv)m/s

Ans-

(i) km/min

(ii) m/min

(iii)km/h

(iv)m/s  √

(10) A car moves with a speed of 40 km/h for 15min and then with a speed of 60km/h for the next 15 minutes. The total distance covered by the car is:

(i) 100km

(ii) 25km

(iii) 15km

(iv)10km

Ans-

The speed of the car in first 15 min = 40km/h

Time taken by car = 15 min

= 15/60

= .25 hour

Distance travelled by car in first 15 min = Time × Speed

= .25 × 40

= 10.00km

The speed of the car in second 15 min = 60km/h

Distance travelled by car in second 15 min = Time × Speed

= .25 × 60

= 15.00km

Total distance = 10 +15

= 25km

(12) Figures given below shows the distance – time graph for the motion of two vehicles A and B. Which one of them is moving faster?

Ans-

Draw a perpendicular CD on time axis to know the distance travelled by cars. It is clear from the figure that A travelled dA distance which is more than distance dB travelled by B.

(13) Which of the following distance – time graphs shows a truck moving with speed which is not constant?

(i)

(ii)

(iii)

(iv)

Ans

(iii) is required answer because it shows non constant movement of truck.

Helping Topics

Motion and Time

Practice sheet, class 7

Displacement

Distance

Time

Acceleration