Answer:
The impulse is -20kg m/s.
Step-by-step explanation:
given mass of ball = 0.4 kg 
The ball is moving towards left with the initial velocity = 30m/s 
The momentum in left direction P1 = mv1 
= (0.4)(30) 
= 12 kg m/s 
The given velocity towards right = -20 m/s ( negative sign shows inverse direction) 
Momentum towards right, P2 = mv2 
P2 = (0.4)(-20) 
P2 = -8 kg m/s 
The Impulse = change in momentum 
= P2 –P1 
= -8-12 
= -20 kg m/s