#$&*

Phy 231

A rubber band begins exerting a tension force when its length is 8 cm. As it is

stretched to a length of 10 cm its tension increases with length, more or less

steadily, until at the 10 cm length the tension is 3 Newtons.

Between the 8 cm and 10 cm length, what are the minimum and maximum tensions?

answer/question/discussion: ->->->->->->->->->->->-> :

0 and 3 N

#$&*

Assuming that the tension in the rubber band is 100% conservative (which is not

actually the case) what is its elastic potential energy at the 10 cm length?

answer/question/discussion: ->->->->->->->->->->->-> :

W = F_Ave * d

W = 1.5 N * 0.02m = 0.03 J

#$&*

If all this potential energy is transferred to the kinetic energy of an initially

stationary 20 gram domino, what will be the velocity of the domino?

answer/question/discussion: ->->->->->->->->->->->-> :

KE = 0.5 * m * v^2

0.03 J = 0.5 * 0.02 kg * v^2

v = 1.73 m/sec

#$&*

If instead the rubber band is used to 'shoot' the domino straight upward, then how high

will it rise?

answer/question/discussion: ->->->->->->->->->->->-> :

PE = m*g*y

0.03 J = 0.02 kg * 9.8 m/sec^2 * y

y = 0.15 m

#$&*

For University Physics students:

Why does it make sense to say that the PE change is equal to the integral of the force

vs. position function over an appropriate interval, and what is the appropriate

interval?

answer/question/discussion: ->->->->->->->->->->->-> :

The force vs. position function can be integrated to yield the work. An integral of any

function over an interval is equal to the average value of that function on the

interval, multiplied by the length of the interval.

#$&*