Question

A 140-g baseball is dropped from a tree 12.0 m above the ground.

If it actually hits the ground with a speed of 8.50 m/s , what is the magnitude of the average force of air resistance exerted on it?

Answer 1

Had there been no air resistance , ball would have hitted the ground by velocity, say v.

From equation of motion we have

V²=u²+2as where u=initial velocity=0,s=distance =12m

a=acceleration (due to gravity ) =9.8m/s²

So we have

V²=0² +2*9.8*12

V²=235.2

V=15.34m/s.

So due to air resistance we have average force =

mass x average acceleration

Average acceleration =Vf-Vi/T

And T from equation of motion is

S=ut+1/2aT²

12=1/2*9.8*T²

T=1.565 s

So average acceleration =15.34-8.50/1.56=4.370m/s²

Average acceleration =0.140*4.370=0.612 N