## Topic outline

• ### Chapter 13 - Motion and Time - 2

• ### Motion and Time

##### Q19. The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.

Ans. Distance between two stations = 240 km

Time taken to cover this distance = 4 hours ##### Q20. A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?

Ans. Number of oscillations = 20

Total time taken to complete 20 oscillations = 32 s ##### Q21. Salma takes 15 minutes from her house to reach her school on a bicycle. If the bicycle has a speed of 2 m/s, calculate the distance between her house and the school.

Ans. Time taken = 15 min = 15 x 60 = 900 seconds

Speed = 2 m/s

Distance = Speed x Time

= 2 x 900 = 1800 m = 1800/1000 = 1.8 km

##### Q22. When pendulum is said to have one complete oscillation?

Ans. The pendulum is said to have completed one oscillation when its bob, starting from its mean position B, moves to A, to C and back to B. ##### Q23. The following Fig. shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster? Ans. Vehicle A is moving faster. Speed of the vehicle is greater if it covers maximum distance in a given interval of time.

##### Q24. Classify the following as motion along a straight line, circular or oscillatory motion:

(i) Motion of your hands while running. Oscillatory motion

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

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

(iv) Motion of a child on a see-saw. Oscillatory motion

(v) Motion of the hammer of an electric bell. Oscillatory motion

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

##### Q25. The odometer of a car reads 57321.0 km when the clock shows the time 08:30 AM. What is the distance moved by the car, if at 08:50 AM, the odometer reading has changed to 57336.0 km? Calculate the speed of the car in km/min during this time. Express the speed in km/h also.

Ans. Distance covered = 57336-57321 = 15 km

Time taken = 8:50 – 8:30 = 20 min Now, convert 20 min into hour = 20/60 = 1/3 h ##### Q26. 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. A car moving with a constant speed. Image from NCERT

A car parked on a side road. Image from NCERT

##### Q27. A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. Calculate the total distance covered by the car.

Ans. Case 1

Speed = 40km/h

Time taken = 15 min = 15/60 = ¼ hours

Distance = Speed x Time = 40 X ¼ = 10 km

Case 2

Speed = 60km/h

Time taken = 15 min = 15/60 = ¼ hours

Distance = Speed x Time = 60 X ¼ = 15 km

Total Distance = 10 km + 15 km = 25 km

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