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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Fill in the Blank

•A 5.0 kilogram toy car is moving at 2.0 meters per second. 

–What is the kinetic energy of the toy car? (Round to the nearest whole number and include your units!!!)

​•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