a stockroom worker pushes a box with mass 11.2 kg on a horizontal surface with a constant speed of 3.5 m/s. the coefficients of kinetic and static
friction between the box and the surface are 0.200 and 0.450, respectively. what horizontal force must the worker apply to maintain the motion of
the box?
22 n
25 n
18 n
30n

22 N

Explanation:

The box is moving, so there is kinetic friction.

The speed is constant, so there is no acceleration.

Draw a free body diagram of the box.  There are four forces.

Normal force Fn pushing up.

Weigh force mg pulling down.

Applied force F pushing right.

Friction force Fn μk pushing left.

Sum the forces in the y direction:

∑F = ma

Fn − mg = 0

Fn = mg

Sum the forces in the x direction:

∑F = ma

F − Fn μk = 0

F = Fn μk

F = mg μk

F = (11.2 kg) (9.8 m/s²) (0.200)

F = 22.0 N

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