1) The force you apply is not constant when you stretch the rubber band. At what
ID: 1434849 • Letter: 1
Question
1) The force you apply is not constant when you stretch the rubber band. At what point in the stretch is the force the least? At what point is the force the greatest?
a. The force is greatest when you first begin to stretch the rubber band and least when it is fully stretched.
b. The force is least when you first begin to stretch the rubber band and greatest when it is fully stretched.
c. The force is greatest when you first begin to stretch the rubber band, least at mid-stretch, and greatest again when it is fully stretched.
d.The force is least when you first begin to stretch the rubber band, greatest at mid-stretch, and least again when it is fully stretched.
2) As you lift the book, assume you lift it at a constant speed. Was the average force that you applied to the book as you lifted it
a. Less than the weight of the book
b. Greater than the weight of the book
c. Roughly equal to the weight of the book
3) Lift a book from the floor to the table. Did you do work? To answer this question, consider whether you applied a force parallel to the displacement of the book.
a. No work is done because I did not apply any force
b. No work is done because I applied a force opposite to its displacement
c. I did work because I applied a force parallel to its displacement
d. I did work because gravity helped me lift the book
4) While holding one end fixed in place, stretch a rubber band. Did you do work on the rubber band? To answer this question, consider whether you applied a force parallel to the displacement of the moving end of the rubber band.
a. No work is done because I did not apply any force
b. No work is done because I applied a force opposite to its displacement
c. I did work because I applied a force parallel to its displacement
d. I did work because the rubber band is very stiff and difficult to stretch
Explanation / Answer
(1)
given that
the force is not constant.
A rubber band can be thought of as a spring (for our purposes) and the force required to stretch a spring is proportional to the distance the spring is already stretched. The greater the stretch, the more force you need to stretch it. So the force is the least when we just starting, and greatest when we have stretched it the most.
answer
b. The force is least when you first begin to stretch the rubber band and greatest when it is fully stretched.
(2) when we lift the book there is only one downward force m*g .
which is equal to the weight of book so the average force that we applied to lift the book
F = mg (upwardly )
answer
c. Roughly equal to the weight of the book
(3) work done for lifting the book = F.d = F d cos(theta )
In given condition force is applied parallel to th displacement so theta is 0.
work done = F d
answer
c. I did work because I applied a force parallel to its displacement
(4)
By the physical definition of work
W = F.d cos(theta)
we do work when we apply a force parallel to the object's displacement.
W = F*d
answer
c. I did work because I applied a force parallel to its displacement
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