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Work and Energy: Jeopardy Review Game Kinetic Energy Potential Energy Machines Work and Power $1 $1 $1 $1 $2 $2 $2 $2 $5 $5 $5 $5 $10 $10 $10 $20 $20 Bungee $5 Calculate the kinetic energy of a 3 kg toy cart that moves at 4m/s. 24 J A hammer falls off a rooftop and strikes the ground with a certain KE. If it fell from a roof that was four times higher, how would its KE of impact compare? Its speed of impact? KE would be 4X greater Speed would be 2X greater Answer this question in terms of KE. Why does a small, lightweight car generally have better fuel economy than a big, heavy car? Smaller mass means less kinetic energy for a given velocity. A rollercoaster starts with a speed of 5.0 m/s at a point 45 m above the bottom of the dip. Neglect friction, what will be the speed of the rollercoaster at the top of the next slope, which is 30 m above the bottom of the dip? 18 m/s 1/2mv2 + mgh = 1/2mv2 + mgh masses cancel out – then you can solve for the velocity at the top of the second hill. What is the minimum speed of the ball at the bottom of its swing (point B) in order for it to reach point A, which is 1.0 m above the bottom of the pendulum? 4.5 m/s What will be the kinetic energy of an arrow having a potential energy of 50J after it is shot from a bow? 50 J What is the potential energy of a spring that has a spring constant of 250 N/m when it is compressed 3.0 cm? 0.11 J A 3.0 kg stone is dropped from a height of 10.0 m, and strikes the ground with a velocity of 7.00 m/s. What average force of air friction acts on it as it falls? 22.7 N If a spring is compressed 0.25 m and when it is released it causes a 5.0 kg block to move 0.45 m/s on a frictionless surface, what is the k value of this spring? What force was exerted on the block? 16 N/m 4.1 N In what two ways can a machine alter an input force? By changing the magnitude or the direction. What is the ideal mechanical advantage of this ramp? 5 What is the ideal mechanical advantage of this pulley system? If it requires an effort force of 1500 N to lift the 500 kg Load what is the % efficiency of the pulley? IMA = 4 83% efficiency What is the IMA of each of the level systems shown? A=1 B=2 C = 0.5 Work is required to lift a barbell. How many times more work is required to lift the barbell three times as high? Three times the work. How much power is required to do 100 J of work on an object in a time of 0.5 s? How much power is required if the same work is done in 1 second? 200 W 100 W True or False: A machine decreases the amount of work done on an object. False! Less force over a greater distance. Chris’s car can go from 0 to 100 km/h in 10 s. If the engine delivered twice the power to the wheels, how many seconds would it take? 5 seconds If a car traveling at 60 km/h will skid 20 m when its brakes lock, how far will it skid if it is traveling at 120 km/h when its brakes lock? 80 m Describe how energy is transferred during a bungee jump. Gravitational PE to Kinetic Energy to Spring Potential Energy then back to KE and gravitational PE