Physics worker pushing crate problem?

[匿名]

2018-05-02 8:28 am

A worker pushes a 32 kg box on a rough floor by a force of 160N at an angle of 25 degrees below the horizontal line. The coefficient of the kinetic friction between the floor and the box is 0.150.

A.) Find the net work done on the box when the box has moved 4.55m.

B.) Assuming that the box starts from rest, what is the speed of the box after it has moved 4.5m. (Answer strictly based on work and energy theorem.)

Also, do you mind showing all steps as to how you get your answer?

回答 (1)

Ash

2018-05-02 9:06 am

✔ 最佳答案

(A)
F(app) along horizontal floor = 160cos25 = 145N
F(app) perpendicular to floor = 160sin25
F(N) = mg - F(app) perpendicular to floor = (32*9.81) - 160sin25 = 246.3 N
F(friction) = μ F(N) = 0.150 * 246.3 = 36.95N

F(net) = F(app) along horizontal floor - F(friction) = 145 - 36.95 = 108N
Work = F(net) x displacement = 108*4.55 = 491.4 J

(B)
Work = F(net) x displacement = 108*4.5 = 486 J
Work, W = ΔKE = KE(final) - KE(initial) =
since box starts from rest KE(initial)=0
W = ½mv²
v² = 2W/m = 2*486/32
v = 5.5 m/s

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