- #1

uchicago2012

- 75

- 0

## Homework Statement

In the figure, a block of mass M slides without friction around the curved track. (a) If the block starts from rest at A, what is its speed at B? (b) What is the force of the track (the normal force) on the block at B?

See Figure 1

## Homework Equations

U

_{f}+ K

_{f}= U

_{i }+ Ki

## The Attempt at a Solution

for a, I was just wondering if this seemed right:

mgh

_{f}+ 1/2mv

_{f}

^{2}= mgh

_{i }+ 1/2mv

_{i}

^{2}

mg(R) + 1/2mv

_{f}

^{2}= mg(4R)

1/2mv

_{f}

^{2}= mg(4 R) - mg(R)

v

_{f}

^{2}= 2g(4R) - 2g(R)

v

_{f}= sqr. root [ 2g(3R) ]

I'm not sure about b. I think the normal force might be zero, but then I think that would mean the block would fall off the track.

F

_{net,x}: N = ma

a = 0 in the x direction, so

N = 0