Question

A ball thrown up is caught by the thrower, 4 seconds after start. The height to which the ball has risen is:
a) 20 m
b) 10 m
c) 400 m
d) 2 m

Answer 1

20 m

Explanation:

final velocity in y direction :0 ( at maximum height)

applying v=u+at

initial velocity in y direction :20

acceleration in y direction :g

time taken:2 s

therefore: s=ut+1/2gt×t=20×2-1/2×10×4

applying this equation we get 20m

we considered y direction .....as the maximum height is along y direction .

time of accent = time of decent in projectile motion

in the question the time is given for the entire journey.but we have to consider only the time taken for half the journey.