U8 ENERGY- WS2 NAME______Per._____

1. Mr. Dominic (on a good day) can bench press 30 kg. A. Draw a force diagram for the 30 kg barbell as he lifts it at constant speed.

B. As Mr. D lifts the barbell, does the force of gravity on the barbell change? ______

C. Draw bar charts showing the energy transfer for the barbell as he lifts it. Before lifting halfway up At its highest point Objects in system:

D. Construct a graph to the right showing the Force of gravity on the barbell (weight) vs. the height it travels (Mr D’s arms Fg (N) are 0.9 m long). (Assume Ediss is negligible.) 400

E. Shade in the area on your graph that represents the Gravitational Potential Energy the barbell gains as Mr. D 200 lifts it. Calculate this amount of Eg. Label this Energy on your graph.

F. Write an equation for how to calculate Eg, based on what you did in part E. 0.2m 0.4m 0.6m 0.8m h (m) Eg =

2. A 36 g pendulum is raised from point B to point A as shown.

A. Identify height = 0 on the scale and calculate the gravitational potential energy (Eg) at point A.

B. Draw quantitative bar charts to show the energy transfer from point A to rulings are 0.5 point B. cm apart

Objects in system:

A v = 0

B rulings are 0.5 cm apart 3. Benji uses 60 J of energy to lift a kitty cat 1.5m. What is the cat’s mass?

4. Jimmy (mass = 75 kg) gains 66.2 J of gravitational potential energy when he jumps 1.5 meters high on Pluto. What is the gravitational field strength on Pluto?

5. A 1500 kg car going 22 m/s stops in 4.5 seconds. A. Calculate its acceleration and the net force on the car. Draw a force diagram for the car while it is braking.

B. Draw qualitative bar charts showing the energy transfer from the time the car begins to brake until it stops. Objects in system:

C. The car’s brakes can stop it over a distance of 25.meters. Using the friction force you calculated in Ff (N) part A, construct a graph of the force of friction vs. 8000 the stopping distance.

D. Shade in the area that represents the energy that is dissipated during braking. 4000

E. Write an equation for how to calculate Edis, based on what you did in part D.

6m 12m 18m 24m distance F. Calculate the energy (Ediss) during braking.

G. To what object(s) is the energy dissipated during braking?

H. What similarities exist between this graph and the one in problem 1D ?

I. Based on these two graphs, how would you define energy? What units are equivalent to a Joule?

6. It took 76 joules of energy for Marquita to travel 8 meters before she stopped while playing on a “Slip ‘n Slide”. How big was the friction force that stopped Marquita?