Work and Energy of wrecking ball

[kaspis245]

Homework Statement

A wrecking ball swings at the end of a 10.0-m cable on a
vertical circular arc. The crane operator manages to give the ball a
speed of 6.00 m/s as the ball passes through the lowest point of its
swing and then gives the ball no further assistance. Friction and
air resistance are negligible. What speed v does the ball have
when the cable makes an angle of 30.0° with respect to the
vertical?

Homework Equations

Gravitational potential energy

The Attempt at a Solution

The answer must be 3.1 m/s

 

[TSny]

When calculating r + k, note that the base of the triangle is not 5 m.

You might try a different construction. Draw a horizontal auxiliary line from the final position of the ball over to the vertical string at the initial position.

 

[kaspis245]

Sorry, I saw my mistake xD .

If I draw a line from initial to final position, I get an isosceles triangle. Still I don't know how to find the height.

 

[TSny]

Here's the horizontal line I was suggesting.

 

[kaspis245]

Solved it, thanks!