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PROBLEM

(II) A box of mass 4.0 kg is accelerated from rest by a force across a floor at a rate of 2.0 m/s22.0 \mathrm{~m} / \mathrm{s}^{2} for 8.0 s . Find the net work done on the box.

STEP 1

1. The box has a mass of 4.0kg4.0 \, \text{kg}.
2. The box starts from rest.
3. The box is accelerated at a rate of 2.0m/s22.0 \, \text{m/s}^2.
4. The acceleration occurs over a time period of 8.0s8.0 \, \text{s}.
5. We need to find the net work done on the box.

STEP 2

1. Calculate the final velocity of the box.
2. Determine the displacement of the box.
3. Calculate the net work done using the work-energy principle.

STEP 3

Calculate the final velocity of the box using the formula for acceleration:
v=u+at v = u + at where u=0m/s u = 0 \, \text{m/s} (initial velocity), a=2.0m/s2 a = 2.0 \, \text{m/s}^2 (acceleration), and t=8.0s t = 8.0 \, \text{s} (time).
v=0+(2.0m/s2)(8.0s) v = 0 + (2.0 \, \text{m/s}^2)(8.0 \, \text{s}) v=16.0m/s v = 16.0 \, \text{m/s}

STEP 4

Determine the displacement of the box using the formula:
s=ut+12at2 s = ut + \frac{1}{2}at^2 Substitute u=0m/s u = 0 \, \text{m/s} , a=2.0m/s2 a = 2.0 \, \text{m/s}^2 , and t=8.0s t = 8.0 \, \text{s} :
s=0+12(2.0m/s2)(8.0s)2 s = 0 + \frac{1}{2}(2.0 \, \text{m/s}^2)(8.0 \, \text{s})^2 s=12(2.0)(64.0) s = \frac{1}{2}(2.0)(64.0) s=64.0m s = 64.0 \, \text{m}

SOLUTION

Calculate the net work done using the work-energy principle:
Wnet=ΔKE=12mv212mu2 W_{\text{net}} = \Delta KE = \frac{1}{2}mv^2 - \frac{1}{2}mu^2 where m=4.0kg m = 4.0 \, \text{kg} , v=16.0m/s v = 16.0 \, \text{m/s} , and u=0m/s u = 0 \, \text{m/s} .
Wnet=12(4.0kg)(16.0m/s)212(4.0kg)(0)2 W_{\text{net}} = \frac{1}{2}(4.0 \, \text{kg})(16.0 \, \text{m/s})^2 - \frac{1}{2}(4.0 \, \text{kg})(0)^2 Wnet=12(4.0)(256.0) W_{\text{net}} = \frac{1}{2}(4.0)(256.0) Wnet=512.0J W_{\text{net}} = 512.0 \, \text{J} The net work done on the box is:
512.0J \boxed{512.0 \, \text{J}}

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