Solving Impulse & Momentum Problems

[Jared944]

Ok, so this problem is kind of complicated, so ask me if you need clarification. This problem deals with Impulse and Momentum.

There are two balls hanging vertically from a horizontal plane. Ball A is pulled back and is set up to strike ball B.
Given for ball A -
mass = 1.5 kg.
Height = .3 m (measured from a horizontal plane from Ball B)
initial speed = 5.00 m/s (as it leaves your hand)
Given for Ball B -
mass = 4.60 kg
speed = 0 m/s (implied)

Question a) is -
Using the principle of conservation of mechanical energy, find the speed of Ball A just before impact.
Question b) is -
Assuming an elastic collision, find the velocities (magnitude and direction) of both balls just after the collision.

I can't quite set up part A, I know I have to integrate a kinematics equation and the principle of conservation of mechanical energy, but I can't quite get it right.
Thanks!

 

[KoGs]

By integrate do you mean calculus and take the integral? Because that is not needed here. This question is to test whether you understand what conservation of energy and conservation of momentum is. If you wouldn't mind, could you please briefly explain to me what these 2 concepts mean?

 

[Jared944]

Ahh, I just figured it out. I was using the wrong set of equations, I am sorry! Part a) can be figured by using the equation -
.5 m(vf^2)+m(g)hf = .5m(v0^2)+m(g)h0

Or, in other words, .5(1.5)(vf^2)+(1.5)(9.8)(0)=.5(1.5)(5^2)+(1.5)(.3)
vf=5.56!

Thanks for the nudge in the right direction!

 

[KoGs]

You should get into the habit of writing out the equation first, before putting in numbers. This way even if you accidently put in the wrong numbers or do the calculations wrong, at least this shows your teacher/professor that you understand what is going on. So he/she will still give you a good mark. And you could even take 1 step further and explain why you are equating the equations you are equating.