NCERT Solutions for Class 7th Science
Chapter 13 – MOTION AND TIME
(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)
Q.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 on a see-saw.
(v) Motion of the hammer of an electric bell.
(vi) Motion of a train on a straight bridge.
Ans (i) Motion of your hands while running – Oscillatory motion
(ii) Motion of a horse pulling a cart on a straight road – Straight line motion
(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 motion
Q.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 kilometres.
(iv) The time period of a given pendulum is not constant.
(v) The speed of a train is expressed in m/h.
Ans (i) The basic unit of time is second - Correct
(ii) Every object moves with a constant speed – Not correct
An object can move with a constant or variable speed.
(iii) Distances between two cities are measured in kilometers - Correct
Q.3 A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?
Q.4 The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.
Q.5 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.
Q.6 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.
Q.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.
Q.8 Which of the following relations is correct?
(i) Speed = Distance × Time (ii) Speed = Distance/Time
(iii) Speed = Time/Distance (iv) Speed =1/(Distance × Time)
Q.9 The basic unit of speed is:
(i) km/min (ii) m/min
(iii) km/h (iv) m/s
Ans (iv) m/s
Q.10 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. The total distance covered by the car is:
(i) 100 km (ii) 25 km
(iii) 15 km (iv) 10 km
Ans (ii) 25 km
Distance covered in first 15 mins at 40 km/h = 40 x 15 / 60 = 10 km
Distance covered in next 15 mins at 60 km/h = 60 x 15 / 60 = 15 km
Therefore, total distance covered by car = 10 + 15 = 25 km.
Q.11 Suppose the two photographs, shown in Fig. 13.1 and Fig. 13.2, had been taken at an interval of 10 seconds. If a distance of 100 metres is shown by 1 cm in these photographs, calculate the speed of the blue car.
Q.12 Fig. 13.15 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?
Q.13 Which of the following distance-time graphs shows a truck moving with speed which is not constant?