cq_1_141

phy201

Your 'cq_1_14.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.

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Seed question 14

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, and what do you think is the average tension?

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

The minimum tension is - 3 newtons the max is + 3 newtons

In think that the average tension would be 3/2 = 1.5

#$&*

How much work is required to stretch the rubber band from 8 cm to 10 cm?

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

'dw= F * 'ds

'dw = 3newtons * 10cm

'dw= 30joules

N * cm is not Joules; N * m is Joules. You need a conversion here.

`dW = F_ave * `ds. The average force isn't 3 Joules.

#$&*

During the stretching process is the tension force in the direction of motion or opposite to the direction of motion?

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

I think tension is the force that is opposing the direction of motion. As the band stretches the tension is what causes it to slow down.

#$&*

Does the tension force therefore do positive or negative work?

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

Tension force does positive work on the systme in the opposite direction

tension force opposes motion. Therefore whichever is positive, tension or displacement, the other is negative and F * `ds gives you a negative result.

#$&*

The rubber band is released and as it contracts back to its 8 cm length it exerts its tension force on a domino of mass .02 kg, which is

initially at rest.

Again assuming that the tension force is conservative, how much work does the tension force do on the domino?

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

#$&*

Assuming this is the only force acting on the domino, what will then be its kinetic energy when the rubber band reaches its 8 cm length?

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

F= m * a

F= .02kg * 9.8m/s^2

F= .196 newtons

Dw= fnet * ds

dw= .196 * .08meters

'dw= .016J

#$&*

At this point how fast will the domino be moving?

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

F= m *a

a = m/f

a= .02kg/.196 newtons

a= .102 m/s^2

#$&*

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about 30 minutes

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&#Please compare your solutions with the expanded discussion at the link

Solution

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