# Physics Question on momentumWatch

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#1
A ball of mass 0.2kg falls from a height of 45m.On stiking the ground it rebounds in 0.1s with two-thirds of the velocity with which it struck the ground.Calculate
1) the momentum change on hitting teh ground
2)the force on the ball due to the impact
0
13 years ago
#2
(Original post by Salman)
A ball of mass 0.2kg falls from a height of 45m.On stiking the ground it rebounds in 0.1s with two-thirds of the velocity with which it struck the ground.Calculate
1) the momentum change on hitting teh ground
2)the force on the ball due to the impact
1)
ball strikes the ground with velocity = v

vÂ² - uÂ² = 2as
vÂ² = 2gs (initial velocity, u = 0)
vÂ² = 2*9.8*45
vÂ² = 882
v = 29.7 m/s
==========

rebound speed w = (2/3)v
= (2/3)*29.7
= 19.8
but ball is now moving in opposite direction so its velocity is -ve, i.e.
w = -19.8 m/s
==========

Momemtum change is
m(v - w)
= 0.2(29.7 + 19.8)
= 0.2*49.5
= 9.9
=====

2)
Impulse = change in momemtum
Ft = 9.9
F*0.1 = 9.9
F = 99 N
=======
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