Unit: Energy
Year: 1994 Question#: 17
Question: A student pulls a block 3.0 meters along a horizontal surface at a constant velocity. The diagram below shows the components of the force exerted on the block by the student.
How much work is done against friction?
(1 ) 18 J
(2 ) 24 J
(3 ) 30 J
(4 ) 42 J
What is this question really asking?
Explanation by: Raphael D
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Answer 1
18 J
INCORRECT
This answer is incorrect because through the correct use of the formula F = FdeltaS one does not find 18 J as the correct answer. It looks as though you used the viertical force times the horizontal displacement. Keep in mind that when calculating work, the force has to cause the change in displacement. An upward force in this case could not move the block sideways. return to top
Answer 2
24 J
CORRECT
This answer is correct because through the correct use of the formula one would multiply 8.0 N by 3.0 m (since thaey are both parallel to each other and the force caused the motion) finding 24 J as the correct answer. return to top
Answer 3
30. J
INCORRECT
This answer is incorrect because there is no way to find 30. J as an answer when unsing the formula W = FdeltaS. return to top
Answer 4
42 J
INCORRECT
This answer is incorrect for the same reason as above. There is no way to find this as an answer if the formula was used correctly. return to top
What's this question really asking?
Do you know how to distinguish which force to use in this problem where there are two different forces?
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