help with motion!

[jaydee]

a rubber ball of mass 80g bounces vertically on a concrete floor at 10m/s and rebounds at 8.0m/s. the time of contact between ball and floor during the bounce was 0.050 s
a) calc the average net force acting on the ball during its contact with the floor
b) calc the average force that the floor exerts on the ball
c) calc the average force that the ball exerts on the floor

two identical bowling balls each of mass 4.0kg move towards each other across a frictionless surface with equal speeds of 3.0m/s. During the collision, 20J of initial kinetic energy is transformed into heat and sound. After the collision the balls move in opposite direction away from each other. what is the speed of each ball after the collision
 
Both are from the heinemann physics 12 textbook! cant seem to get my head around em..much appreciated if someone could help out!

[Lasercookie]

a) You know mass and the time of contact. You also know the initial velocity and the final velocity.
You can figure out the change in it's momentum.
The change in momentum is the impulse. 
From this you can then figure out the force.

b) You can figure out the acceleration.
Apply Newton's second law.
You could, if you want, set the force of the floor on the ball to be negative. (so that your answer to c) would be positive).

c) Newton's third law, use magnitude of force from b)

[Lasercookie]

two identical bowling balls each of mass 4.0kg move towards each other across a frictionless surface with equal speeds of 3.0m/s. During the collision, 20J of initial kinetic energy is transformed into heat and sound. After the collision the balls move in opposite direction away from each other. what is the speed of each ball after the collision

Didn't notice this one.

Kinetic energy in the system is lost during the collision. This means that it's an inelastic collision.
So while kinetic energy is not conserved, momentum is still conserved.

This means you can still apply your regular conservation of momentum equation.
Net initial momentum = Net final momentum
You should be familiar with this.

[jaydee]

thanks for the advice!