Question

A strong-armed physics student throws a tennis ball vertically. The ball stays in the air for 5.5 seconds. Assuming the ball left from the ground, how fast did it leave his hand?

Answer 1

Answer:

27.5 m/s

Explanation:

applying motion equations we can find the answer,

v = u + a*t

Let assume ,

u = starting speed(velocity)

v = Final speed (velocity)

t =  time taken for the motion

a = acceleration

by the time of reaching the highest point subjected to the gravity , the speed should be equal to zero  (only a vertical speed component is there)

for the complete motion it takes 5.5 s. that means to reach the highest point it will take 5.5/2 =2.75 seconds

we consider the motion upwards , in this case the gravitational  acceleration should be negative in upwards (assume g=10 m/s2)

that is,

v = 0 , a = -10$ms^{-2}$    , t =2.75

v = u + at

0 = u -10*2.75

u = 27.5 $ms^{-1}$