A ball is thrown at an angle of 30° to the horizontal. The initial kinetic energy of the ball is K. Air resistance has a negligible effect on the motion of the ball.What is the kinetic energy of the ball at the maximum height?

A. 0

B. 0.25K

C. 0.75K

D. 0.87K

The answer is C but I don't understand how to get the answer. Please help!

A. 0

B. 0.25K

C. 0.75K

D. 0.87K

The answer is C but I don't understand how to get the answer. Please help!

Original post by zscc

A ball is thrown at an angle of 30° to the horizontal. The initial kinetic energy of the ball is K. Air resistance has a negligible effect on the motion of the ball.What is the kinetic energy of the ball at the maximum height?

A. 0

B. 0.25K

C. 0.75K

D. 0.87K

The answer is C but I don't understand how to get the answer. Please help!

A. 0

B. 0.25K

C. 0.75K

D. 0.87K

The answer is C but I don't understand how to get the answer. Please help!

Simple trig for the velocity. At the peak, the vertical velocity is zero and the horizontal velocity is unchanged (so resolve the initial velocity).

Original post by mqb2766

Original post by zscc

A ball is thrown at an angle of 30° to the horizontal. The initial kinetic energy of the ball is K. Air resistance has a negligible effect on the motion of the ball.What is the kinetic energy of the ball at the maximum height?

A. 0

B. 0.25K

C. 0.75K

D. 0.87K

The answer is C but I don't understand how to get the answer. Please help!

A. 0

B. 0.25K

C. 0.75K

D. 0.87K

The answer is C but I don't understand how to get the answer. Please help!

Simple trig for the velocity. At the peak, the vertical velocity is zero and the horizontal velocity is unchanged (so resolve the initial velocity).

But what do I do after getting the initial velocity?

Original post by zscc

Simple trig for the velocity. At the peak, the vertical velocity is zero and the horizontal velocity is unchanged (so resolve the initial velocity).

But what do I do after getting the initial velocity?

The initial velocity is v (30 degrees to the horizontal), so what is the horizontal velocity and then how are the KEs related?

Original post by mqb2766

But what do I do after getting the initial velocity?

The initial velocity is v (30 degrees to the horizontal), so what is the horizontal velocity and then how are the KEs related?

The initial velocity is Kcos30 I think, and KE is directly proportional to speed^2

Original post by zscc

The initial velocity is v (30 degrees to the horizontal), so what is the horizontal velocity and then how are the KEs related?

The initial velocity is Kcos30 I think, and KE is directly proportional to speed^2

If v is the velocity, then I agree the horizontal is vcos(30). So you should know that trig value and as you say KE is proportional to velocity squared ...

Original post by mqb2766

The initial velocity is Kcos30 I think, and KE is directly proportional to speed^2

If v is the velocity, then I agree the horizontal is vcos(30). So you should know that trig value and as you say KE is proportional to velocity squared ...

Ohh sorry typo I meant vcos30. I get it now thx

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