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Name: _________________________________ GP: Work, Power & Energy AP Physics – McNutt Date: ___________ Period: __________ Conservation of Energy Review Solve the problems using appropriate equations and provide all units. 1.) 50 kg gymnast comes to a stop after tumbling. Her feet do 10,000 J of work to stop her. What was the girl's velocity when she began to stop? Formula & Givens Input Numbers & Show Your Work Solution Rearrange KE = ½ mv2 = 20m/s KE = ½ mv2 v2 = KE/ ½ m = 10,000J / ½ (50kg) M = 50kg = 10,000/25 = 400 sqrt 400 = 20m/s KE = 10,000J 2.) A 20-N force is exerted on a box, moving it 40 m in the same direction. What is the magnitude of work done on the box? 20 N 40m Formula & Givens Input Numbers & Show Your Work Solution W=Fxd W= (20-N)(40m) = 800J 800J F = 20 N D =40m 3.) Conveyor belts are often used to move packages around warehouses. A conveyor moves packages at a steady 4.0 m/s. A 500N employee decides to catch a ride by sitting on a 1,000 N box for a 50 m trip: What is the work done by the employee on the box? Formula & Givens Input Numbers & Show Your Work Solution Ha! Gotcha! This is a The employee is doing no work, man, he’s just Your answer is 0 trick question… hitching a ride on the box. The conveyor belt is doing all the work. 4.) A 1,000 kg car is initially at rest. The engine starts and provides 10,000 J of work on the car. What is the final velocity of the car? Formula & Givens Input Numbers & Show Your Work Solution KE = 1/2mv2 KE = 1/2mv2 (10,000 J) = ½(1,000kg) v2 2.236 m/s v2 = (10,000 J) / ½(1,000kg) = 10,000J/2000 v2 = 5 → √5 = 2.236 m/s 5.) A power-lifter raises a 1,000 N weight a distance of 2.0 meters in 0.5 seconds, what is his power output? Formula & Givens Input Numbers & Show Your Work Solution W=Fd P = (1000-N)(2.0m)/0.5s = 4000 Watts 4000 Watts P = W/t 6.) According to the Law of Conservation of Energy, we cannot create new energy. We can, however, convert find new ways to convert energy into usable forms and energy in less time to increase power. Provide an example of how we do both of the above. _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ 7.) Calculate the potential energy of a 6 kg bowling ball suspended 3 m above the surface of the Earth. Formula & Givens Input Numbers & Show Your Work Solution PE = mgh PE = (6kg)(9.8)(3m) = 176.4J 176.4J 8.) A tennis ball launcher works by using a spring to propel the ball forward as shown below: One model of tennis ball launcher has advertised that it is capable of imparting 15,000 J of kinetic energy to a 0.5 kg ball initially at rest. A student carefully measures the compression of the spring to be 0.10 m. What is the elastic energy stored in the spring? Formula & Givens Input Numbers & Show Your Work Solution PE1 + KE1 = PE2 + KE2 k = spring constant x = 0.10m KE = 15,000 J 9.) What is the value of the spring constant for the tennis ball launcher according to the data provided? Formula & Givens Input Numbers & Show Your Work Force = F = kx F = load applied on the spring = mg m = 0.5 kg g = 9.8 m/sec^2 k = spring constant x = 0.10 m Force = F = kx Solution