Q19 of 37 Page 22

A football is kicked into the air vertically upwards. What is its

(a) Acceleration, and (b) velocity at the highest point?



Acceleration will always point downward, and it will be due to gravitational force.


At the highest point, ball will stop for some infinitesimally time and change its direction. Therefore at that time velocity will be zero.


More from this chapter

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17

A particle is projected in air at some angle to the horizontal, moves along parabola as shown in Fig. 4.4, where x and y indicate horizontal and vertical directions, respectively. Show in the diagram, direction of velocity and acceleration at points A, B and C.


 18

A ball is thrown from a roof top at an angle of 45° above the horizontal. It hits the ground a few seconds later. At what point during its motion, does the ball have

(a) Greatest speed.


(b) Smallest speed.


(c) Greatest acceleration?


 20

A, B and C are three non-collinear, non-co-planar vectors. What can you say about direction of A × (B × C)?

 21

A boy travelling in an open car moving on a levelled road with constant speed tosses a ball vertically up in the air and catches it back. Sketch the motion of the ball as observed by a boy standing on the footpath. Give explanation to support your diagram.