Physics 20 Work and Energy Unit Assignment

4/8/18

Name: ______

P20 Unit C UA pt B: Date: ______Work and Energy

1. The units of work is usually joules [J]. Express this unit two other ways, showing appropriate formulas for unit derivation. (1 mark)

2. Roger lifts a 170 g hockey puck to a height of 65.0 cm above the surface of a table. Roger calculates the PE of the puck as 1.08 J. However, after measuring the height of the table to be 1.12 m, LD disagrees with Roger’s answer. a) Show how Roger calculated his answer. (1 mark) b) Determine what PE LD believes the puck would have. (1 mark) c) Who is correct? Explain your answer to receive full marks. (1 mark)

3. Nicole and Ashley are in a fight. Instead of saying gravitational potential energy, Nicole always says potential energy. Ashley insists this is incorrect.

Which student is correct? Explain your reasoning using principles learned in class. (2 marks)

4. The Barringer crater in Arizona was created by a meteor impact. It is estimated that the meteor had a radius of 40 m and a mass of approximately 2.6 x 108 kg, and that it struck the Earth at a speed of nearly 7.20 x 104 km/h. a) What was the KE of the meteor at the instant of impact? (5.2 x 1016 J) (1 mark) b) When one tonne (t) of TNT explodes, it releases about 4.6 x 109 J of energy. In terms of tonnes of TNT, how much energy did the meteor impact have? (1.1 x 107 t) (1 mark)

5. The spring constant for a particular spring is 750 N/m. a) How far must you stretch the spring to store 45.0 J of energy in it? (0.346 m) (1 mark) b) If you wanted to double the amount of elastic potential energy stored in the spring, how much further would you need to stretch the spring? Show two different approaches to calculating your answer. (0.144 m)(2 marks)

6. A weightlifter drops a dumbbell on his toe. When the bell hits his toe, it has a speed of 3.2 m/s. From what height was the dumbbell dropped? (0.52 m) (1 mark)

7. Tarzan is running at a speed of 3.5 m/s and grabs a long vine that is hanging vertically from a tree. How high can the student swing? (0.62 m) (1 mark)

LD Industries 4/8/18

Use the following diagram to answer the next question.

8. A toy car (m = 2.00 kg) starts from rest at point A and slides along the track shown above. The track is frictionless. a) What is the speed of the car at point D? (4.4 m/s) (1 mark) b) What is the total mechanical energy at point B? At point C? (1.6 x 102 J) (1 mark)

9. A motor must generated 9.50 kW to move a car at a constant speed of 25.0 m/s. What is the force of friction on the car? (380 N) (1 mark)

Use the following information to answer the next question.

10. In the diagram, block A is at rest on a frictionless incline. It is attached to block B over a pulley. Block A has a mass of 4.50 kg and block B has a mass of 5.50 kg. When the system is released, block A moves up the incline 1.5 m, after which it has a speed of 3.00 m/s. a) What is the change in PE of block A (hint: recall pullies from unit II) (36 J) (3 marks) b) What is the change in height through which block A moved? (0.81 m) (1 mark)

Bonus Questions: Answer only ONE!!!

Fair Bonus Question: What is a kilowatt hour and how does it relate to power?

Unfair Bonus Question: Evaluate and state the significance please:

LD Industries