3.2.2 Work/Energy Principle

3.2.2 Work/Energy Principle

​•potential energy: STORED ENERGY

–can be in a FIELD or DEVICE

•gravitational PE is stored in gravitational fields

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•elastic PE is stored in elastic objects (springs)

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Multiple Choice

•A 30 kilogram object is positioned 2.0 meters above the surface of the Earth. 

–What is the gravitational potential energy of the object?

• 15 J

• 60 J

• 147 J

• 588.6 J

Multiple Choice

•The length of a spring with a spring constant of 100 newtons per meter is changed by 4.0 centimeters. 

–What is the elastic potential energy stored in the spring?

• 0.08 J

• 2 J

• 200 J

• 800 J

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​•kinetic energy: ENERGY OF MOVING OBJECTS

–depends on mass and velocity

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​•internal energy: TEMPERATURE/HEAT

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​Q

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​When work is done ‘on a system’ there is a net gain of one or more types of energy by that system.  Energy types can change within a system.

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Draw

A car is moving along a flat surface with an increasing speed.  What type(s) of energy are changing? Indicate with arrows for increase/decrease or an 'X' for remains the same

Draw

A car is moving up an incline with constant speed.  What type(s) of energy are changing? Indicate with arrows for increase/decrease or an 'X' for remains the same

Draw

A car is applying its brakes and slowing down as it moves down a slope.  What type(s) of energy are changing?

Draw

A cart is moving on a flat surface toward a wall and is stopped by a spring on its front. What type(s) of energy are changing?

Draw

A rocket flies upward with an increasing velocity [ignore air resistance]. What type(s) of energy are changing?

Multiple Choice

•A 75kg bicyclist coasts down a hill at a constant speed of 12m/s. What is the KE of the bicyclist?

• 4.5E3J

• 9.0E3J

• 5.4E3J

• 1.1E3J

Multiple Choice

•How much work is done by the force lifting a 0.1kg hamburger vertically upwards at a constant velocity 0.3m from a table?

• 0.03J

• 0.01J

• 0.3J

• 0.4J

Multiple Choice

•When a mass is placed on a spring with a spring constant of 60.0 N/m, the spring is compressed 0.500 m. How much energy is stored in the spring?

• 60.0J

• 30.0J

• 15.0J

• 7.50J

Multiple Choice

A spring stores 10.J of elastic potential energy when it is compressed 0.20m. What is the spring constant of the spring?

• 5.0E1 N/m

• 1.0E2 N/m

• 2.5E2 N/m

• 5.0E2 N/m