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Physics work being done?

A crate of mass 50 kg is drug across the floor by pulling on it by a rope that makes an angle of 40deg. above the horizontal. The coefficient of kinetic friction between the crate and the floor is. Uk=0.15

If the crate is pulled a distance of 150 m. at a constant speed of 2.5 km/h,

find

A. the work done by the rope,

B. the work done by the normal force,

C. the work done by gravity,

D. the work done by friction,

E. the total work done.

3 Answers

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  • 9 years ago
    Favorite Answer

    A) W=Fdcosθ, force done by the rope is equivalent to the force of friction so the magnitude of the horizontal forces can be zero (balanced) and speed can remain constant (Newton's First Law). Force of friction = F(normal)*(coefficient) = mg*(coefficient) = 50kg*(9.8m/s^2)*(.15) = 73.5N. W=73.5N(150m)cos(40)

    =8446Nm

    B) W=Fdcosθ, the normal force vector is 90 degrees to the displacement vector. cos(90) = 0. W=Fd(0)

    = 0Nm

    C) The normal force is the equal and opposite force that the Earth exerts back on the object (Newton's Third Law). Since the object is pushing straight down on the earth (not on a slope), the normal force = force of gravity. So answer is the same as B)

    = 0Nm

    D) W=Fdcosθ, we calculated force of friction in A). W=73.5N(150m)cos(180) = 73.5N(150m)(-1)

    = -11025Nm

    E) Total work done is simply the magnitude or sum of all the work done on the system. so ΣW=W(rope) + W(friction) = 8446Nm + (-11025Nm) = -2579Nm

    = -2579Nm

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    5 years ago

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  • 9 years ago

    A. Work done by rope = work done by friction + 1/2* m* v^2

    B. 0

    C. 0

    D. 0.15* m* g* 150

    E. Total work done = work done by the rope

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