- #1

sireh

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## Homework Statement

The coefficient of friction between the block of mass m

_{1}= 3.00kg and the surface in Figure P7.22 is μ

_{k}= 0.400. The system starts from rest. What is the speed of the ball of mass m

_{2}= 5.00 kg when it has fallen a distance of h = 1.50m?

## Homework Equations

This is in the chapter on conservation of energy, so

U

_{i}+ K

_{i}+ ΔE

_{mech}= U

_{f}+ K

_{f}

## The Attempt at a Solution

Using downward direction as positive so g is positive

m

_{2}gh - fh = 1/2(m

_{1}+ m

_{2})v

^{2}

(5.00kg)(9.8m/s

^{2})(1.5m) - (-11.76N)(1.5m) = 1/2(3.00kg + 5.00kg)v

^{2}

91.14Nm = 4kg * v

^{2}

22.785Nm

^{2}/s

^{2}= v

^{2}

4.77m/s = v

That's not the answer that I'm seeing on the answer sheet. I'm not sure what I did wrong.