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Question

the initial velocity of a 4.0 kg box is 11m/sec due west. after the box slides 4.0m horizontally, its speed is 1.5 m/sec. determine the magnitude and the direction of the non-conservative force acting on the box as it slides.

Answer 1

Using conservation of energy,
initial KE=1/2*4*11^2
after 4.0 m
KE'=1/2*4*1.5^2
The kinetic energy was lost due to a force resisting the westward motion, which is eastward.
-F*4.0
(The 4m is the displacement)


Using conservation of energy
1/2*4*11^2-F*4.0=1/2*4*1.5^2
F=1/2*(11^2-1.5^2)
=59.375N

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Answer 2

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Answer 3

First you need the acceleration. Use
V^2 = Vo^2 + 2*a*s (Vo is original velocity, s is distance)

Then use F = m*a

If the sign is positive, the direction is in the direction of Vo; if negative, the opposite direction.