# PHYS310 Lab 9 Work and Energy

Lab 9: Work and Energy

Exercise 9.1

Both kinetic and potential energy are part of the thrill of roller coasters. For this exercise, you will examine the path of a roller coaster

and describe what type of energy is at work.

Questions: use the figure above to complete the following

1. Describe the kinetic and potential energy at each point of the roller coaster path:

2. Between which points is the force of gravity doing positive work on the coaster? Negative work?

3. What happens to the roller coaster’s kinetic energy between points B and C? What happens to its potential energy between these

points?

4. Why is it important for A to be higher than C?

5. If the roller coaster starts at point A, can it ever go higher than this point? What causes the roller coaster train to lose energy over its

trip?

Experiment 9.1: Popper Physics

A popper toy stores energy when you invert it, and releases energy when it “pops” into the air. In this lab, students will calculate the

potential and kinetic energy of a popper toy using simple formulas.

Questions

1. What is the gravitational potential energy your popper has at its maximum height you measured? Use g = 9.8 m/s, and a mass of 0.01

kg.

E p = mgh =

2. Use the following kinematics equations from Labs 4 and 5 to calculate the initial velocity of the popper based on the time ( t ) it is in

the air:

where the final height h = 0 and initial height ho = 0 after the popper travels the total time up and down over your measured time t.

3. Use this value for the initial velocity to find the kinetic energy of the popper right as it “pops” up.

4. Compare your answers for potential energy and kinetic energy. Are they the same, or close to the same?

5. Is the actual energy stored in the popper rubber before it “pops” more or less than the energy the popper has at its highest point?

Why?

Experiment 9.2: Stored Energy

In this lab you will learn about the applications of the conservation of energy by creating your own stored energy toy!

Materials

• *Empty coffee or oatmeal can with plastic lid

• Skewer

• 2 rubber bands (may need larger ones)

• 2 Steel bolts

• 2 Push pins

Questions

1. What is happening inside the can that converts kinetic energy to potential energy? What form of potential energy is this?

2. How is the stored energy converted back to kinetic energy?

3. What function does the suspended mass have? Why is it crucial that this is a relatively heavy object?

4. Let’s say your can has covers a distance of 3 m in 5 seconds under constant acceleration. Use kinematics equations and Newton’s

second law to calculate:

a) the acceleration of the can,

b) the net force on the can,

c) the work required to apply this force over the given distance, and

d) the power required to do this work over the given time. Use a can mass of 500 g.

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