Question

Fisica 9A Cerros < Trabajo C Exercise 5.16 (IE) Part A A student could either pull or push, at an angle of 30" from the horizontal, a 45 kg crate on a horizontal surface, where the coefficient of kinetic friction between the crate and surface is 0.15. The crate is to be moved a horizontal distance of 22 Compared with pushing, pulling requires the student to do work less the same Submit Request Answer Part B Calculate the minimum work required for both pulling and pushing Express your answers using two significant figures separated by a comma 80 AE RO? Wallin, W i-

Answer 1

Part (a) - less because it will reduce the amount of normal force and that will reduce the amount of friction force.

Part (b) -

minimum work will be done when net force is zero. so

Pulling:

F_net = F cos 30 - μmg + μF sin 30 = 0

F = μmg/[cos 30 + μ sin 30]
= 70.296 N

Minimum work done by the student = Horizontal component of force * distance traveled

Minimum work required = 70.296 cos 30 * 22
                                      = 1339.312 J

Pushing:

F net = F cos 30 - μmg - μF sin 30 = 0

F = μmg/[cos 30 - μ sin 30]
   = 83.626 N

Minimum work done by the student = Horizontal component of force * distance traveled

Minimum work required = 83.262 cos 30 * 22
                                        = 1593.282 J

answer ;- 13 x 10² , 16 x 10² J

you can see from the answer in part b that pulling work is less.

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