Revised seed 151

course PHY 121

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?

8*3=24

10*3=30

###This should be 0 for minimum tension and 3 Newtons for maximum tension

answer/question/discussion:

• 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?

100/10=10

###’dW=F_ave*’ds ‘dW= 1.5N*2cm=3N*cm

answer/question/discussion:

• 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?

20/10=2

###This is 1/2mv^2=KE which would be v=sqrt(2*KE/m)=sqrt(2*.03Joules/.02Kg)=1.7m/s^2

answer/question/discussion:

• If instead the rubber band is used to 'shoot' the domino straight upward, then how high will it rise?

###This would be ‘dy=.03Joules/mg=.03Joules/.02kg*9.8m/s^2=.15m

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Good revision.