Conservation of Mechanical Energy?

Question

A child on a 5.00 m long swing has a speed of 4.00 m/s at the bottom of the swing. What angle will the swing make with the vertical when the child reaches his highest point in the swing?

I think that the child has no potential energy in the beginning and has no kinetic energy at the end, but i dont know what to do then.

Answer 1

Pe=Ke
mgh= 0.5 m V^2
h=V^2 / (2g)
sin(A)=(R-h)/R

A=arcsin((R-h)/R)
A=arcsin((R-[V^2 / (2g)])/R)
A= arcSin((5 - [ 4^2 /(2 x 9.81)]/5)
A= 55.5 deg

And by the way your assumption that:"I think that the child has no potential energy in the beginning and has no kinetic energy at the end, but i dont know what to do then." is correct. [ the total energy is conserved.]