BackA red ball has a mass of 250 g. A constant force pushes the red ball horizontally and launches it at a speed of 15 m/s. The same force pushes a green ball through the same distance, launching it at 25 m/s. What is the mass of the green ball?
A pitcher accelerates a 150 g baseball from rest to 35 m/s. How much work does the pitcher do on the ball?
(II) At an accident scene on a level road, investigators measure a car’s skid mark to be 78 m long. It was a rainy day and the coefficient of friction was estimated to be 0.30. Why does the car’s mass not matter?
A car traveling at a velocity v can stop in a minimum distance d. What would be the car’s minimum stopping distance if it were traveling at a velocity of 2v?
A 55 kg softball player slides into second base, generating 950 J of thermal energy in her legs and the ground. How fast was she running?
A 1.60-m-tall person lifts a 1.65-kg book off the ground so it is 2.20 m above the ground. What is the potential energy of the book relative to How is the work done by the person related to the answers in parts (a) and (b)?
A baggage handler throws a 15 kg suitcase along the floor of an airplane luggage compartment with a speed of 1.2 m/s. The suitcase slides 2.0 m before stopping. Use work and energy to find the suitcase's coefficient of kinetic friction on the floor.
A 66.5-kg hiker starts at an elevation of 1150 m and climbs to the top of a peak 2660 m high. What is the minimum work the hiker must do?
A 50 kg ice skater is gliding along the ice, heading due north at 4.0 m/s. The ice has a small coefficient of static friction, to prevent the skater from slipping sideways, but μk = 0. Suddenly, a wind from the northeast exerts a force of 4.0 N on the skater. Use work and energy to find the skater's speed after gliding 100 m in this wind.
A 25-g projectile is fired into a cube of ballistic gel at a velocity of 360 m/s. If the projectile penetrates 15 cm into the gel before stopping, find the average force exerted by the gel onto the projectile. Use the work-energy principle.
CALC A 2.6 kg block is attached to a horizontal rope that exerts a variable force Fx = (20 − 5x) N, where x is in m. The coefficient of kinetic friction between the block and the floor is 0.25. Initially the block is at rest at x = 0 m. What is the block's speed when it has been pulled to x = 4.0 m?
How much work does an elevator motor do to lift a 1000 kg elevator a height of 100 m?
(II) How much work would be required to move a satellite of mass m from a circular orbit of radius r1 = 2rE about the Earth to another circular orbit of radius r2 = 3r_E? (rE is the radius of the Earth.)
An airplane pilot fell 370 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 82 kg and his terminal velocity was 45 m/s, estimate the work done by the snow in bringing him to rest.
A 20 kg child is on a swing that hangs from 3.0-m-long chains. What is her maximum speed if she swings out to a 45° angle?