Q16 of 24 Page 59

A motorcyclist drives from A to B with a uniform speed of 30 km h–1 and returns back with a speed of 20 km h–1. Find its average speed.

Let the distance (AB) = x


Total distance = x + x = 2x


Speed = distance/time


t1 = x/30


t2 (return trip) = x/20


Total time taken = t1 +t2


Total time taken = x/30 + x/20


= (2x +3x)/60


= 5x/60


= x/12


Average speed = total distance/total time taken


= 2x /


= (2x) x


= 24 km/hr


More from this chapter

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14

A girl walks along a straight path to drop a letter in the letterbox and comes back to her initial position. Her displacement–time graph is shown in Fig.8.4.

Plot a velocity–time graph for the same.


 15

A car starts from rest and moves along the x-axis with constant acceleration 5 m s–2 for 8 seconds. If it then continues with constant velocity, what distance will the car cover in 12 seconds since it started from the rest?

 17

The velocity-time graph (Fig. 8.5) shows the motion of a cyclist. Find

(i) its acceleration


(ii) its velocity and


(iii) the distance covered by the cyclist in 15 seconds.


 18

Draw a velocity versus time graph of a stone thrown vertically upwards and then coming downwards after attaining the maximum height.