Calculating force for a mass in a hoop

[Smartguy94]

Homework Statement

A mass M of 6.40E-1 kg slides inside a hoop of radius R=1.60 m with negligible friction. When M is at the top, it has a speed of 5.25 m/s. Calculate the size of the force with which the M pushes on the hoop when M is at an angle of 37.0°.

[URL]http://loncapa.gwu.edu/res/msu/physicslib/msuphysicslib/13_EnergyConservation/graphics/prob25_1015hoop2.gif[/URL]

Homework Equations

Finding the F

The Attempt at a Solution

i tried 2 times and both are wrong

first i tried

a=v^2/r
a=(5.25)^2/1.6
a=17.227

F=ma
F=(.640)(17.227)
F=11.025N and that's wrong...

second try i draw force diagram and got

tan(37)=opposite/adjacent
tan(37)mg=opposite
4.726N=the horizontal force of the gravity? and its wrong.

 

[Doc Al]

first i tried

a=v^2/r
a=(5.25)^2/1.6
a=17.227

You're using the speed at the top. But you need the speed at 37°. Figure that out first.

(FYI: Your diagram is not viewable.)