Calculating Impulse: Tennis Ball Rebound at 45 Degrees | Homework Help

[runningirl]

Homework Statement

A tennis ball of mass m=0.060 kg and speed v=25 m/s strikes a wall at a 45 angle and rebounds with the same speed at 45 degrees. What is the impulse given the wall?

Homework Equations

The Attempt at a Solution

.06(25)(cos30)+.06(25)(sin30)?

i actually had no idea...

 

[collinsmark]

.06(25)(cos30)+.06(25)(sin30)?

i actually had no idea...

Impulse is the change in momentum, so you're on the right track. But why use 30^o in your trig functions? The problem statement says the angles are both 45^o.

 

[runningirl]

sorry, i mean 45. but is my method correct?

 

[collinsmark]

sorry, i mean 45. but is my method correct?

Essentially, yes, your method works. But I would pick one trig function (either sine or cosine) and stick with it. In general, the one you pick depends on how the angle is defined -- with respect to the wall's surface or the wall's normal. Of course in this particular problem, with the angle being 45^o, you'll get the same answer either way. But generally speaking for similar, future problems, you'll have to use the correct one.