# Centered projectile motion

1. Sep 30, 2008

### oscar_lai_hk

A mass is attached to one end of the massless string, the other and of which is attached to a foxed support. The mass swings around in a vertical circle as shown in Fig 5.36. Assuming that the mass has the minimum speed necessary at the top of the circle to keep the string from going slack, at what location should you cut the string so that the resulting projectile motion of the mass has its maximum height located directly above the center of the circle.

2. Sep 30, 2008

### tiny-tim

Hi oscar_lai_hk!

Show us what you've tried, and where you're stuck, and then we'll know how to help.

3. Sep 30, 2008

### oscar_lai_hk

I can write the equation towards the center : T + mg cos0 = mv^2/R
and I consider the energy at the moment of escape and the highest position
I get the equation (0.5)mv^2 = (0.5)m(vcos0)^2 + mgy
then I try to diff. the above equation of y respect to the angle 0
it is right?

4. Sep 30, 2008

### tiny-tim

Hi oscar_lai_hk!

I'm really not following that.

Start by putting T = 0 at the top of the loop to find out what vtop is.

Then find out what vθ is, at any angle θ.

The split vθ into horizontal and vertical components …