NCERT Solutions For Class 7 Science Chapter 13 Motion and Time

Among the given distance-time graphs, following graph shows the movement of a truck with speed which is not constant:

It is so because in this graph vehicle is not covering equal distances in equal intervals of time.

The steps to be followed are as follows:

1. Find the distance travelled by blue car in photographs by measuring distance taking mid-points of car in following manner:

(Here, distance may vary in centimeters due to difference in the size of photographs taken. So, follow only the method for finding right answer, which may vary.)

2. According to the question, 1 cm is equivalent to 100 m.

Therefore, distance travelled = 0.5 cm x 100m = 50m

3. Speed = distance travelled / time taken

Therefore, speed = 50m / 10s = 5 m/s

Correct option is (iv).

Explanation: Speed is the distance traveled per unit of time. The standard unit of distance is metre (m) and standard unit of time is second (s).

Correct option is (ii).

Explanation: Speed is the distance traveled per unit of time.

Among the vehicles, vehicle A is moving faster than B. It is so because A has travelled greater distance in shorter period of time in comparison to that of vehicle B. Vehicle B has moved lesser distance in greater period of time as depicted in graph.

Average speed of car = (40 km/h + 60 km/h)/2 = 50 km/h

Total distance travelled = speed × total time taken = 50 km/h × (½) h = 25 km/h

1. The shape of the distance-time graph for the motion of car with constant speed will be as follows:

2. The shape of the distance-time graph for the motion of car parked on a side road will be as follows:

Time taken by Salma = 15 min = 15 × 60 s = 900 s

Speed of bicycle = 2 m/s

Let the distance between school and house be x m

Distance travelled = time taken × speed

∴ Distance, x = 900 s × 2 m/s = 1800 m = 1.8 km

$\begin{array}{l}\text{Time period of a simple pendulum is the time taken to complete one oscillation.}\\ \text{The time period is given by,}\\ \text{Time period = }\frac{\text{Time taken}}{\text{Number of oscillations}}=\frac{32\mathrm{s} }{20}=1.6 \mathrm{s}\end{array}$

Following statements are not correct:

(ii) Every object moves with a constant speed.

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