Posted by Alex on Sunday, May 18, 2008 at 4:28pm.
A 3.0kg air puck sliding at 4.0m/s collides with a 5.0kg puck. After the collision the 3.0kg puck is moving north at 1.0m/s while the 5.0kg puck is moving south at 1.0m/s.
a) What was the initial velocity of the 5kg puck?
I did:
m1v1 + m2v2 = m1v1' + m2v2'
(3)(4) + (5v2) = (3)(1) + (5)(1)
and got 0.8m/s for v2.
b) What percentage of the initial kinetic energy remained after the collision?
I did
KE1' + KE2'

KE1 + KE2
and got 16%
Now these questions I'm completely lost with because of the angles.
2) A 3kg ball moving east strikes a 2kg ball that is moving east at 2m/s. Following the collision the 3kg ball moves at 4m/s in a direction [E55S] while the other ball moves in a direction of [E35N].
a) By considering components of momentum in a NS direction, calculate the speed that the 2kg ball had after the collision.
b) By considering conservation of momentum in an eastwest direction, find the initial speed of the 3kg ball.
3) A 20kg child sitting on smooth ice is sliding straight north at 2m/s when she throws a big 2kg snow ball which (after the throw) moves [N60E] at 10m/s.
a) Calculate the momentum, speed and direction of motion of the child following the throw.

Physics  Damon, Sunday, May 18, 2008 at 4:54pm
2) A 3kg ball moving east strikes a 2kg ball that is moving east at 2m/s. Following the collision the 3kg ball moves at 4m/s in a direction [E55S] while the other ball moves in a direction of [E35N].
a) By considering components of momentum in a NS direction, calculate the speed that the 2kg ball had after the collision.

a)
Initial momentum N is zero
final momentum N:
0 = 2 (s sin 35)  3 (4 sin 55)
s = 12 sin 55 / 2 sin 35 = 9.83/1.15
s = 8.55 m/s
=========================
b) By considering conservation of momentum in an eastwest direction, find the initial speed of the 3kg ball.

initial momentum E = 3 v + 2*2 = 4 + 3 v
final momentum E = 2*8.55 cos35 + 3*4 cos 55
so
4+3v = 14+6.88
3 v = 16.88
v = 5.63

Physics  Maddie, Monday, April 22, 2013 at 9:40am
What about the answer to #3?
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