Physics questions, no rush

Test Preparation AP Test Preparation
1

<p>At the top of a loop the loop, you are weightless, how heavy due you feel at the bottom.
Answer = 6mg
Show that is you hold a string horizontal with a mass at the end, and a peg is under the latching point, it has to be less than 2/5 the way down so that the mass makes a complete circle.
Also, does anyone know a site that shows acceleration of a two block stacked system. When there is friction between the two blocks and a force is applied to either the top one or the bottom one.</p>

<p>m=50kg,
T = 5000N
two supports 10m apart.
Rope = 10m above the ground.
a) the sag in the rope when the m is on the middle of the string, and b) the change in potential energy, which is solved from a.
If anyone can show some of the work or some hints on how to solve them Id be happy. Thanx in advanced.</p>

2

<p>At the top of the loop mg+Fn = mv^2/r and Fn=0 so
v= sqrt(gr) and the energy = .5*mv^2 = .5mgr + mg2R
At the bottom of the loop potential = 0
so 2.5mgr = 1/2mv^2
v^2 = 5gr so the forces are
mv^2 / r + mg = m5g + mg = 6mg. This was in a different book that my teacher had.</p>