Which of the following individuals described below does the most work? Ignore fr

Question

Which of the following individuals described below does the most work? Ignore friction for all cases. a. Kelsey who exerts a force of 600 N on a stationary car that won't move in 2.0 seconds. b. Jarrod who lifts a 46 kg box to a height of 2.0 meters off the ground in 5.0 seconds. c. Mark who pushes a crate across the floor 1.5 meters with a force of 550 N in 3.0 seconds 30 d. Katie who pushes a crate (m 50 kg) with a force of 300 N along an incline a distance of 3.5 meters (along the incline in 4.0 seconds. e. Kelly who pulls on a cart (mass 25 kg) with a force of 400 N at an angle of 30 degree (relative to the horizontal) through a horizontal distance of 3.0 meters in 4.5 seconds.

Explanation / Answer

(a)

Since the car doesn't move, displacement is zero.

so work done W = F.d = 0, as d = 0

Kelsey does zero work.

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(b)

Jarrod lifts the box to 2 meters in 5s, so acceleration of the box is given by,

S = (1/2)at2

or, 2m = (0.5)a(5s)2

or, a = 0.16 m/s2

So if force applied by Jarrod is F, then motion of the box says,

F - mg = ma

or, F = m(g+a) = (46kg)(9.8m/s2 + 0.16m/s2)

or, F = 458.16 N

Work done by Jarrod, W = F.d = (458.16 N).2m

or W = 916.32 J

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(c) Force applied by Mark is F = 550N

Displacement of the crate is d = 1.5 m

So work done is W = F.d = (550N)(1.5m)

or, W = 825 J

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(d)

Katie applies force F = 300N and produces displacement d = 3.5 m

So work done is W = F.d = (300N)(3.5m)

or, W = 1050 J

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(e)

Kelly applies a horizontal force F = (400N)cos300 = 346.4 N

displacment d = 3m

So, work done W = F.d = (346.4N)(3m)

or, W = 1039.23 J

So, from the data of work done in the five cases above, it's clear that maximum work is done by Katie.

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This concludes the answers. Check the answer and let me know if it's correct. If you need any more clarification or correction, feel free to ask.....

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