Question

A ball was struck with a force of 200 N, so it bounced at 400 m / s. The batter touched the ball within 0.2 seconds. The ball mass is

Answer 1

F= 200 N
v = 400 m/s. 
t   =0.2 second 

F = ma
F = mv/t
200 = m 400/0.2
m= 200/2000
m = 0.1 kg

Answer 2

we know,
Force = mass × acceleration
also ,
acceleration = change in velocity by time

here
F = 200 N
v( final ) = 400 m/s
t = 0.2

initial velocity = 0
so, change in velocity = ( v - u) = 400m/s

hence ,

F = m( v - u)/t

200 = m × ( 400 )/0.2

200 = m × ( 2000)

m = 0.1 kg = 100g