Question

In a football match a goal attempt by Messi is stopped by neuer in 0.2 sec . If the mass of the ball is 400gram and the net force applied by neuer is 120N .what was the speed by which Messi hit the ball?

Answer 1

here we can use these equations

impulse = force *time
=change in momentum = p2-p1
and we know that momentum P = mass *velocity = m*v

here impulse force applied by neuer= 120 N
and the time required to stop the ball =0.2 sec

we want to find the initial velocity of the ball
we can use the relation

force*time = change in momentum
= P2-P1
where P1=initial momentum P2 = final momentum
we know that the ball is stopped ,that is its final momentum= mass*final velocity = m*0 = 0
now
force*time = 0-initial momentum momentum
(initial momentum =mass*initial velocity = 0.4 kg * v
120*0.2 = -0.4* v
v = -120*0.2/0.4
=- 60 m/s
there fore the velocity of ball = 60 m/s toward the neuer