A ball (I) having a mass of 0.3 kg and moving at a speed of 4.9 strikes a glancing blow on a stationary ball (

Ask neil tyson degrassi

We know that energy must be conversed, so momentum will do the same.
We'll use the equation below to ultimately set up and solve the problems provided.

M(1)'*V(1)'+M(2)'*V(2)'=M(1)*V(1)+M(2)V…

Where M=mass, V=velocity and the little ' (on the left side of the equation) simply mean "the original".
So the original mass and velocity of ball one and the original mass and velocity of ball two will be equal to the final mass and velocities of the two balls added together.

So starting with the left side of the equation, we see M(1)' is 0.3kg, and it's velocity is 4.9m/s.
We also see M(2)' is unknown, but since it's velocity is zero, that part of the equation will go away.
So now we have the following;

(0.3kg)*(4.9m/s)+0=M(1)*V(1)+M(2)V(2)

The question then tells us that after the blow, ball one, M(1) is now moving at 4.5m/s.
So lets plus that in as well. Since it is after the blow, it will be on the right side of the equation.

(0.3kg)*(4.9m/s)+0=(0.3kg)(4.5m/s)+M(2)…

Awesome. So part A of the problem asked for the momentum of ball two, M(2).
Momentum is simply mass times velocity. Since we know all other parts of the equation, we can now solve for the momentum of ball two. In doing so...

(0.3kg)*(4.9m/s)+0-(0.3kg)(4.5m/s)=M(2)…

Lets simplify.

0.12kgm/s=M(2)V(2)

Awesome. So there's the answer to part A.

Now for part B:

Since we now know that 0.12kgm/s=M(2)V(2) we can use that in this question.
They tell us they now find V(2) to be 13.3m/s. So we can simply rearrange the equation find the mass of ball two, or M(2).

0.12kgm/s=M(2)*(13.3m/s) so.... (0.12kgm/s)/(13.3m/s)=M(2)=0.009kg.

So there you go. And I see you have the directions figured out fine, so you should be able to put these two together easily.