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 N-S direction, calculate the speed that the 2kg ball had after the collision.

b) By considering conservation of momentum in an east-west 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 N-S 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 east-west 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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