Calculate the original speed of the cue ball

[panders3]

A 0.40-kg cue ball makes a glancing blow to a stationary 0.30-kg billiard ball so that the cue ball deflects with a speed of 1.2 m/s at an angle of 30.0º from its original path. Calculate the original speed of the cue ball if the billiard ball ends up traveling at 1.5 m/s.

from its original path. Calculate the original speed of the cue ball if the billiard ball ends up traveling at 1.5 m/s.




I think i just use conservation of momentum here pt initial = pt Final? But the 30.0º from it's original path is throwing me off does it even come into it?

 

[Doc Al]

I think i just use conservation of momentum here pt initial = pt Final?

Good.

But the 30.0º from it's original path is throwing me off does it even come into it?

Remember that momentum is a vector. Consider components parallel and perpendicular to the original direction of the cue ball. (You'll end up with 2 equations, one for each component.)

 

[panders3]

Because my original vector is in only one dimension let's say east then the north of one vector has to equal the south of the other vector. Correct?

Plug in the numbers and solve?

 

[Doc Al]

Because my original vector is in only one dimension let's say east then the north of one vector has to equal the south of the other vector. Correct?

Yes. Since the initial total momentum is zero in the north-south direction, those components of the final momenta must cancel.

Plug in the numbers and solve?

The above will give you one equation. You'll need another for the east components of the final momenta.

 

[panders3]

and they need to equal the total of the initial vector.

 

[Doc Al]

and they need to equal the total of the initial vector.

Sure. Total momentum is conserved.