A person in good physical condition can put out 100 W of useful power for several hours at a stretch, perhaps by pedaling a mechanism that drives an electric generator. Neglecting any problems of generator efficiency and practical considerations such as resting time: (a) How many people would it take to run a 5.00 kW electric clothes dryer? people (b) How many people would it take to replace a large electric power plant that generates 800 MW? people

please help with questions 18,19 and 20

A 0.50-kg book slides on a horizontal table top. The kinetic friction force on the book has a magnitude of 1.2N. (a) how much work is done on the book by friction during displacement of 4m to the right? (b) The book now slides 4m to the left, returning to its starting point. During this second 4-m displacement, how much work is done on the book by friction? (c) what is the total work done on the book by friction during the complete round trip? (d) on the basis of your answer to part (c), would you say that the friction that the force is conservative or non-conservative? Explain.

A certain rain cloud at an altitude of 1.50 km contains 3.20 x 10' kg of water vapor. How long would it take for a 2.36-kW pump to raise the amount of water from Earth's surface to the cloud's position?

(a) Compute the electrical energy used by a household whose monthly electrical bill is $34, computed at the rate of $0.07 per kWh. (b) How long could this energy be used to burn ten 60 W light bulbs? (c) If this energy were used to raise a car of mass 1965 kg, to what height would the car be raised?

(a) What force must be supplied by an elevator cable to produce an acceleration of 0.800 m/s2against a 200-N frictional force, if the mass of the loaded elevator is 1500 kg? (b) How much work is done by the cable in lifting the elevator 20.0 m? (c) What is the final speed of the elevator if it starts from rest? (d) How much work went into thermal energy?

An box with mass of 2kg is pulled from the bottom of a 30 deg ramp to the top, a distance of 3 meters measured along the surface of the ramp. How much work was done by gravity during displacement of the box?

Because of friction, a constant force of 20 N is needed to slide a box across a room to the right at a constant speed: a) How many Newtons must the friction force be? b) How much work is done by the friction force? c) How much work is done by gravity? d) How much work is done by the normal (upward) force? e) What is the net work done?

Calculate the amount work is done by the engine of a 9000 kg truck if it accelerates from 5 m/s to 18 m/s? If the engine performs this acceleration in 8 seconds, calculate the power that the engine delivers.

An electric hoist working at 65% efficiency lifts 255 kg to a height of 6.5 m drawing 1470 W of power. Assuming a constant speed, how long did it take to raise the mass?