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July 24, 2014

July 24, 2014

Posted by **Jamila** on Tuesday, June 13, 2006 at 12:30pm.

What is the work Ws done on the cart by the string?

(the cart is on the table attached to a pulley from which a block is hanging)

After the block has fallen 1 m, potential energy of M2 g H = 3*9.8*1 = 29.4 J is converted to kinetic energy of both the cart and the block. Since they will both be travelling at the same speed, and the cart has 2/3 of the total mass, only 2/3 of the potential energy loss acts to accelerate the cart. That would be 19.6 J.

You could get the same result by solving two free body equations to get the tension in the string, and multiplying it by the distance moved.

T = M1 g = M2 a

M2 g -T = M1 a

M2 g = (M1 + M2) a

a = g [M2/(M1 + M2)]

T = M2 a = M2 g * [M2/(M1 + M2)]

= 2/3 * M2 g

d

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