Transcript Chapter 9
Chapter 9 Energy Question • Calculate the change in kinetic energy when the speed of a 10 kg cart increases from 4 m/s to 10 m/s Answer • 420 J Question • How much work is done by a person who picks up a 3 kg crate from the floor and raises it 2 m? Answer • 60 J Question • At one point in its fall, a falling object has a kinetic energy of 5 J and a potential energy of 10 J (relative to the floor). It continues to another point where its potential energy is 3 J. What is its kinetic energy at this point? Answer • 12 J Question • A pole vaulter wishes to clear a 4 m bar. How fast must she run? (Neglect energy that heats the pole and assume that all her kinetic energy is converted to gravitational potential energy.) Answer • 8.9 m/s Question • A person atop a 30 m cliff throws a ball at 4 m/s at an angle of 37 degrees above the horizontal. How fast does the ball hit the ground? (use conservation of energy) Answer • 24.8 m/s Question • Daniel’s mass is 100 kg and he climbs a 4.3 m high flight of stairs in 5.4 seconds. How much power does he exert in doing so? Answer • 796 W Question • A cart moving at 25 m/s possesses 428 J of kinetic energy. What is the mass of the cart? Answer • 1.4 kg Question • A shiny new 180 kg motorcycle sits at the edge of a 35 m cliff. The gravitational potential energy at the base of the cliff is zero. What is the gravitational potential energy at the top of the cliff? Answer • 63,000 J Question • Work is done on a cannonball by the force from gunpowder exploding in a cannon. Assume the average force is 3500 N while it is pushed 2.2 m inside the barrel. What is the kinetic energy gained by the cannonball? Answer • 7700 J Question • Two people, both of mass 60 kg, ascend a 5 m high staircase. Person A does it in 10 s and person B does it in 15 s. Who does more work? Answer • Equal amounts of work are done Question • Work is done lifting a barbell. How much work is done lifting a twice-as-heavy barbell twice as far? Answer • Four times as much Question • What are the units of work? Answer • Joule Question • Energy is the ability to do _______. Answer • work Question • What are the 2 types of mechanical energy? ( 1 point each) Answer • Potential and kinetic Question • When work is done on an object, _____ is transferred to that object. Answer • Energy Question • What is potential energy due to? Answer • position Question • What is kinetic energy due to? Answer • motion Question • Which has a greater affect on an object’s kinetic energy, a change in mass or a change in speed? Answer • Change in speed Question • Two machines do the same amount of work. How can one machine be more powerful than the other? Answer • The more powerful machine does the work in less time. Question • What is the unit of power? Answer • Watts Question • For a moving car, if the speed of the car doubles, by how much does its kinetic energy increase? Answer • 4 times Question • True or False: When you push against a heavy refrigerator and it does not move, you are not doing work. Answer • True Question • How much work is needed to lift an object that weighs 200 N to a height of 4 m? Answer • 800 J Question • How much power is needed to lift a 200 N object to a height of 4 m in 4 s? Answer • 200 W Question • A person is bungee jumping. Originally, they have 15000 J of gravitational potential energy. Some time after they jump, their gravitational potential energy drops to 3750 J. What is their kinetic energy at this position? Answer • 11250 J Question • For a pendulum, where is gravitational potential energy a maximum? Draw a picture. Answer • At its high points Question • As you descend a hill on a roller coaster, what energy transfer takes place? In other words, energy is converted from what to what as you descend? Answer • From gravitational potential energy to kinetic energy Question • A 2000 kg car is traveling at 11 m/s when it suddenly slams on the brakes to stop. If the car skids for 10 m, what retarding force do the brakes produce? Answer • 12,100 N Question • A car that travels twice as fast as another when braking to a stop will skid _______ as far. Answer • Four times Question • A toy cart moves with a kinetic energy of 40 J. What will its kinetic energy be if its speed is doubled? Answer • 160 J