Finding distance with the conservation of energy equation

[asdf12321asdf]

Homework Statement

3. A baseball (m = 0.150 kg) is thrown with an initial speed of 30.0 m/s at an angle of 37.0 degrees from the horizontal at y = 0 m. (a) Find the initial KE of the ball. (b) Use conservation of energy (not kinematic equations) to find the maximum height reached by the ball. (Hint: Does the ball have any velocity at its maximum height?)

Homework Equations

KE_f + U_f = KE_i + U_i
(.5)mv_f² + mgy_f = (.5)mv_i² + mgy_i

The Attempt at a Solution

(a) Part a I got the correct answer, but can you tell me if I did it the correct way. I did (.5)(0.15)(30)² = 67.5J

(b) What I tried was using KE_f + U_f = KE_i + U_i . For the velocity at the top I accounted for the angle and got that the velocity in the x direction was 24.0m/s So I did:

(.5)(0.15)(24.0)² + (.5)(9.8)y = 67.5 (from part a) + (0.15)(9.8)(0)

Solving for y I get 4.96m, but that is not the correct answer. I'm not sure if I am doing it the wrong way or if I made some error somewhere, so any help would be appreciated.

Thanks

 

[brushman]

You did 'a' correctly.

For 'b', check your Uf.

 

[asdf12321asdf]

Oh wow, thanks a lot. I changed the m in Uf to .15 and then got 16.6m which is the correct answer. It's unfortunate I've spent all this time on this problem due to this small error, though it's reassuring to know I was doing it the right way at least. Thanks again!