Work, Power, Energy

When is work done on an object?

• When an object has a net force applied to it.

• When an object moves while a net force is being applied to it

• When an object doesn't move while a net force is applied to it

• When an object is moving without a net force being applied to it

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When the weightlifter holds the weight above his head he may get incredibly tired, ...

• He is getting tired because he is doing work on the barbell of weights

• He is getting tired because his muscles are stretching and squeezing to do work on the barbell of weights

• He is now the equivalent of a table with weights on it.

• He is getting tired because his muscles are stretching and squeezing, but he is not doing work on the barbell of weights

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What just happened in this picture?

• The weight lifter did work by lifting the barbells from the floor to above his head.

• The weight lifter did not do work when lifting the barbells above his head.

• The weight lifter did no work because he is just a table for weights.

• The barbells did work on the weight lifter when lifted from the ground to above the weight lifters head.

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Which of the following examples has NO work being done? (Choose all that apply)

• An archer stretches her bowstring.

• An ant carries a leaf cutting from a tree to his colony

• An athlete does push-ups on the ground

• A book sits on the shelf

• An asteroid speeds across the solar system

Which of the following examples has work being done? (Choose all that apply)

• An archer stretches her bowstring.

• An ant carries a leaf cutting from a tree to his colony

• An athlete does push-ups on the ground

• A book sits on the shelf

• An asteroid speeds across the solar system

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The units of measurement for work are?

• Newton

• Newton*meter

• Joule

• Watt

• Joule per second

A kilojoule is how many joules?

• 1

• 100

• 10,000

• 100,000

• 1,000

A megajoule is how many joules?

• 1

• 100,000

• 1,000

• 1,000,000

• 100

Suppose that you apply a 100 Newton horizontal force to a box on the floor, which pushes the box 10 meters. How much work do you do on the box?

• 100 J

• 1 J

• 1000J

• 10000J

• 1 kJ

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How do you calculate power?

• Amount of work done divided by the time interval during which the work is done.

• Amount of net force applied to an object multiplied by the distance the object moves

• Mass multiplied by acceleration

• Amount of momentum gained multiplied by the time interval in which the momentum was gained