Question

A ball weighing 25 grams is thrown vertically into the air. it takes 15 seconds to reach its highest point. how much time would it take to reach the ground from its highest point?

Answer 1

We use the kinematic equations of vertically projected body to solve this question .

The equations are as below.

V=u + at
S =ut + 1/2at^2
2as=v^2-u^2

Since we do not have V we use the relationship below to get V

F=ma=1/2mv^2

0.025kg × 10=0.25N

1/2 × 0.025 ×v^2=0.25

0.0125v^2=0.25

V^2=20
V=4.472m/s

Using equation 1) we vet:

4.472=0+10t

t=0.4472seconds.

Answer 2

 Solution - 
                 Ball covers equal distance in equal time interval ,Because gravitational acceleration is same in both condition , when it is going upward or coming back downward.
         So if ball takes time 15 seconds to reach highest point , it will take again 15 seconds to reach ground from maximum height .