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5.67 - Force Question

by TDS1988
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Mar5-11, 06:07 PM
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1. The problem statement, all variables and given/known data

What horizontal force must be applied to the cart (of mass M) shown in Figure P5.67 so that the blocks remain stationary relative to the cart? Assume all surfaces, wheels, and pulley are frictionless. Notice that the force exerted by the string accelerates m(1).

Figure P5.67:
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2. Relevant equations

Sum of forces on m(1):

1) T = m(1)*a

2) m(2)*g - T = m(2)*a

3) a = F / [M + m(1) + m(2)]

3. The attempt at a solution

Well, I first created the above equations. I substituted T (from equation 1) into 2), which gave me:

a = [m(2)*g] / [m(1) + m(2)]

I then subbed this into equation 3, which gave me:

F = m(2)*g*[M+m(1)+m(2)] / [m(1) + m(2)]

The book's answer is nearly the same thing, except that it's only m(1) in the denominator:

F = m(2)*g*[M+m(1)+m(2)] / m(1)

Thanks in advance for the help :)

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Mar5-11, 06:29 PM
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The magnitude of the acceleration of m2 vertically with respect to the ground is NOT the same as the magnitude of the acceleration of m1 horizontally with respect to the ground.

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