Power

Which statement correctly defines power?

A motor does 15 000 J of work in 60 s. What is the power of the motor?

A pump operates at a power of 800 W. Calculate the time it takes the pump to do 120 000 J of work.

A 1.5 kW kettle is switched on for 4.0 minutes. What is the energy transferred by the kettle?

One watt is equivalent to which of the following?

Machine X does 10 000 J of work in 25 s. Machine Y does 10 000 J of work in 50 s. Which statement correctly compares the two machines?

A crane does 48 000 J of work in 2.0 minutes. What is the power of the crane?

A light bulb has a power rating of 60 W. How much energy does it transfer in 5.0 minutes?

An electric heater is rated at 3.0 kW. It transfers 540 000 J of energy. For how long was the heater switched on?

A student says: “My phone charger transfers 50 000 J of energy, so it must be very powerful.” State and explain whether the student is correct. Which response best evaluates the student’s reasoning?

A student measures that an engine does 36 000 J of work. The engine’s power is 600 W. The student claims the engine ran for 6.0 minutes. Determine whether the student’s claim is correct.

A machine does work at a constant rate. If the work done by the machine is tripled while the time taken remains the same, what happens to the power?

A runner and a weightlifter both transfer 6000 J of energy. The runner does this in 10 s and the weightlifter does this in 3.0 s. What is the difference in power between the two?

Two identical water pumps each do 200 000 J of work. Pump A operates at 500 W and Pump B operates at 250 W. A technician needs both pumps to finish at the same time. Pump A is switched on at time zero. How long before time zero should Pump B be switched on?

A hiker climbs a hill, transferring energy at a rate of 200 W for 15 minutes. The hiker then rests and descends, doing no work against gravity. A cyclist covers the same hill in 3.0 minutes, transferring the same total energy as the hiker. What is the power of the cyclist during the climb?

Which pair of quantities has the same numerical value for a given process?

A 0.50 kW motor is used to lift a load. The motor runs for 2.0 minutes and does 48 000 J of work on the load. Calculate the percentage of the motor’s total energy output that is used to do work on the load.