Energy Review Test Key

Name: Kay Date: Period: Unit 5 Review - Energy Essential Skills that will be tested 1. Fill in the following table information. | Variable Name | Variable Symbol | Unit Name | Unit Symbol | Formula | On Reference Sheet? | |---|---|---|---|---|---| | gravitational potential energy   | PE | Joule | J | PE = mgh | yes | | kinetic energy | KE | Joule | J | KE = 1/2 mv² | yes | | work | W | Joule | J | W = FΔx | no | | power | P | Watt / Joule/sec | W | P = W/t | no | | force | F | Newton | N | n/a | n/a | | mass | m | Kilogram | kg | n/a | n/a | | weight/force due to gravity | Fg, W | Newton | N | Fg = mg | yes | | acceleration due to gravity | g | meters per second per second | m/s² | g ≈ 9.8 m/s² | yes | | velocity | v | meter per second | m/s | n/a | n/a | | displacement | Δx | meter | m | n/a | n/a | Circle the appropriate choice that makes the statement true. 2. At an object's maximum height, kinetic energy is zero / maximum while the potential energy is zero / maximum.   3. At an object's lowest point, kinetic energy is zero / maximum while potential energy is zero / maximum. 4. Mass affects / does not affect the amount of total energy. 5. As an object falls under the influence of gravity,   potential energy increases / decreases / remains the same. 6. As an object falls under the influence of gravity, total mechanical energy increases / decreases / remains the same. 7. As an object falls under the influence of gravity, total energy increases / decreases / remains   the same. 8. An object traveling   faster and faster while not changing height has a kinetic energy that increases / decreases / remains the same and a total mechanical energy that increases / decreases / remains the same.   9. As an object falls under the influence of gravity, kinetic energy and potential energy are equal everywhere / at the halfway point only.   10. As an object falls under the influence of gravity, potential energy is greater than kinetic energy after halfway point / before the halfway point. 11. As an object falls under the influence of gravity, potential energy is less than kinetic energy after halfway point / before the halfway point.   12. Answer the following questions: a. A 10 kg object is traveling at 20 m/s while another object whose mass is 15 kg is traveling at 10 m/s. Who has greater kinetic energy? How do you know? KE₁ = 1/2(10)(20²) = 2000 J KE₂ = 1/2(15)(10²) = 750 J * The object moving faster because of the KE equation. 13. A 2 kg ball is dropped from a height of 36 m. Calculate the total mechanical energy, potential energy and kinetic energy for this journey. 36 m: PE = 720 J KE = 0 J 2/3 h: PE = 475 J KE = 245 J 1/2 h: PE = 360 J KE = 360 J 1/3 h: PE = 238 J KE = 482 J 1/6 h: PE = 120 J KE = 600 J 0 m: PE = 0 J KE = 720 J 14. All of the following ramps are 5 m high. Which block will be moving the fastest when it reaches the bottom? Explain. Same speed at bottom because all start with the same initial energy. 15. Calculate the kinetic energy of a 700 kg truck moving at 30 m/s. KE = 315,000 J 16. A typical Boeing 737 has a mass of approximately 60,000 kg. Calculate the gravitational potential energy of the plane when it is 9000 m in the air. PE = 5.4 x 10^9 J 17. What is the law of conservation of energy? Energy must not be created or destroyed so total energy at beginning must be equal to total energy at end. 20. A bird is flying 15 m above the water when it spots its prey and dives down towards its prey at 5 m/s. Calculate how fast the bird is going when it snatches its prey at the surface of the water. v = 18 m/s 21. A ball is rolling across the floor at 8 m/s when it starts up a ramp. Calculate the maximum height the ball rolls up the ramp. h = 3.2 m 22. A 63-kg downhill skier is moving with a speed of 13 m/s as he starts his descent from a level plateau at 123-m height to the ground below.   What his speed when he is halfway down the hill?   v = 37 m/s 23. A 20 kg box is pushed with a force of 75 N up a 3 m long ramp into the back of a truck over the course of 5 seconds. a. Calculate the work done on the box. W = 225 J b. How much gravitational potential energy does the box have at the top of the ramp? PE = 225 J c. Calculate the height of the truck. h = 1.1 m d. The box is then accidentally pushed off the edge of the truck. How much kinetic energy does the box have right before it hits the ground?   KE = 225 J e. Calculate the velocity of the box right before it hits the ground. v = 4.7 m/s f. Calculate the power exerted in moving the box up the ramp. P = 45 W Questions from http://www.physicsclassroom.com/reviews/energy/energyprint.cfm 11. A 1200 kg car and a 2400 kg car are lifted to the same height at a constant speed in an auto service station. Lifting the more massive car requires:   a. less b. the same c. twice as much d. four times as much e. more than 4 times as much Answer: c. twice as much work. 12. An arrow is drawn back so that 50 joules of potential energy is stored in the stretched bow and string. When released, the arrow will have a kinetic energy   of: a. 50 J b. more than 50 J c. less than 50 J Answer: a. 50 J due to the conservation of energy.