1. A cord is used to lower vertically a block of mass M a distance d at a constant downward acceleration of g/4. (a) Find the work done by the cord on the block. (b) Find the work done by the work of gravity. 2. A child pulls a 5.6 kg box a distance of 12 m along a horizontal surface at a constant speed. What work does the child do on the box if the coefficient of kinetic friction is 0.20 and the cord makes an angle of 450 with the horizontal? 3. To push a 25 kg crate up a 270 incline, a worker exerts a force of 120 N, parallel to the incline. As the crate slides 3.6 m, how much work is done on the crate by: (a) the worker, (b) the force of gravity, and (c) the normal force due to the incline?
1. A cord is used to lower vertically a block of mass M a distance d at a constant downward acceleration of g/4. (a) Find the work done by the cord on the block. (b) Find the work done by the work of gravity.
2. A child pulls a 5.6 kg box a distance of 12 m along a horizontal surface at a constant speed. What work does the child do on the box if the coefficient of kinetic friction is 0.20 and the cord makes an angle of 450 with the horizontal?
3. To push a 25 kg crate up a 270 incline, a worker exerts a force of 120 N, parallel to the incline. As the crate slides 3.6 m, how much work is done on the crate by: (a) the worker, (b) the force of gravity, and (c) the normal force due to the incline?
4. A projectile with a mass of 2.4 kg is fired from a cliff 125 m high with an initial velocity of 150 m/s, directed 41.0º above the horizontal. What are (a) the kinetic energy of the projectile just after firing and (b) its potential energy? (c) Use conservation of energy to find the speed of the projectile just before it strikes the ground.
5. A 220-lb man jumps out a window into a fire net 36 ft below. The net stretches 4.4 ft before bringing him to rest and tossing him back into the air. What is the potential energy of the stretched net if no energy is dissipated?
6. A body of mass m starts down from the top of an inclined plane 20 ft long and 10 ft high. What is its velocity at a point 12 ft from the top if coefficient of friction is 0.1?
7. Two snow-covered peaks are at elevations of 862 m and 741 m above the valley between them. If a skier starts from rest on the higher peak and just coasted down without exerting any effort, at what speed would he arrive at the lower peak?
8. Starting a race, a 68.2-kg sprinter runs the first 7.04 m in 1.60 s, starting from rest and accelerating uniformly. What average power does the sprinter generate during the 1.60-s interval?
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