Two horses pull a large crate of negligible mass at constant speed across a barn

Question

Two horses pull a large crate of negligible mass at constant speed across a barn floor by means of two light steel cables. A large box of mass 250 kg sits on the crate (see the figure below, which shows a top-down view of the crate and box). As the horses pull, the cables are parallel to the horizontal floor. The coefficient of friction between the crate and the barn floor is 0.25.

(a) What is the work done by each horse if the box is moved a distance of 28 m?
kJ

(b) What is the tension in each cable if the angle between each and the direction the crate moves is 12°?
kN

Explanation / Answer

b)

The speed is constant , then a = 0 . So:
2 * T cos12° = 0.25 * 250 * 9.8
T = 313 N

a)

The work done by each horse is :
W = 0.5 * 0.25 *250 * 9.8 * 28 = 8575N

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