- #1

qball1982

- 5

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## Homework Statement

A ball attached to a massless rope is allowed to swing around a circle of radius r=0.8m. When the ball reaches point B, the horizontal rope hits the peg P causing the ball to swing around a smaller circle.

A.)If the ball is started at A with a speed of 6m/s, at what position x should the peg P be placed to allow the ball to just make it past the point C. Hint: Rope tension at C will be zero, the rope remains straight at point C, and ignore air resistance.

B.) If there were air resistance, how much work would be required for it to stop the ball at point B? Assume m=2.2kg.

## Homework Equations

A. 1/2mv

_{1}

^{2}+mgy

_{1}=1/2mv

_{2}

^{2}+mgy

_{2}

a

_{rad}=v

^{2}/r

v

_{min}

^{2}=rg or r=v

_{min}

^{2}/g

B.W

_{total}= K

_{2}-K

_{1}

## The Attempt at a Solution

So I calculated the value of v at point B by using:

1/2mv

_{1}

^{2}+mgy

_{1}=1/2mv

_{2}

v=4.508m/s

But I don't know how to get from point B to C.

B.) I used W

_{total}=K

_{2}-K

_{1}

W

_{total}=-39.6

air resistance=-39.6-(-9.8*0.8)=-31.76 J

Is that a correct way to work part B?