# Conservation of Energy of Mass on Crane

## Homework Statement

A mass is suspended from a crane by a cable of length L. The crane and the mass is moving at constant speed V. The crane stops and the mass on the cable swings out.

What is the angle that the mass swings?
If the angle is 50 degrees and L=6m, what is the initial speed of the crane?

## The Attempt at a Solution

For the first part where it asks for the angle, since no numbers are given I assume they're just asking for the equation. My attempt at this is using the equation PE=mgh where h=L(1-cosθ) so it'll be PE=mgL(1-cosθ). The second part for the initial speed can be solved by (PE + KE)initial =(PE+KE)final.

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billy_joule

## The Attempt at a Solution

For the first part where it asks for the angle, since no numbers are given I assume they're just asking for the equation. My attempt at this is using the equation PE=mgh where h=L(1-cosθ) so it'll be PE=mgL(1-cosθ).
It's likely you're expected to express θ in terms of L and V (and g), m will cancel out. You'll use the same equation you will for the second part.

The second part for the initial speed can be solved by (PE + KE)initial =(PE+KE)final.
Yes, just plug and chug.