Power

A builder raises eight slabs from the ground onto the back of a lorry that is 1.5 m above the ground. The complete time for this is 48 s, and the weight of each slab is 200 N. What useful power does the builder generate?

May/June 2015

A $100\ \text{W}$ lamp is turned on for five hours each day over a period of three weeks. The price of one unit of electricity is $\$0.24$. What is the cost of running the lamp for this period?

May/June 2016

A small motor is rated at an input power of $10\,\text{W}$ and operates for $5.0\,\text{minutes}$. How much electrical energy is supplied to the motor during this period?

May/June 2017

A small hydroelectric power station channels water away from a river. Each second, $20\,\text{kg}$ of water passes through a pipe and drops through a vertical height of $15\,\text{m}$. The efficiency of the power station is $0.60$ (60%). The gravitational field strength is $g = 10\,\text{N kg}^{-1}$. What is the power output?

May/June 2017

A small motor has an input power rating of $10\,\text{W}$ and is operated for $5.0\,\text{minutes}$. How much electrical energy is supplied to the motor over this period?

May/June 2017

A student works out his power when running up a staircase. He measures the vertical height of the stairs, the time taken to run up them and his weight. How does he calculate his power?

May/June 2018

What is the unit name and numerical value represented by mW?

May/June 2018

A student proposes three separate definitions of power. Which of these definitions are accurate?

May/June 2019

A set of solar panels has a combined area of $12\,\text{m}^2$. For every $1.0\,\text{m}^2$ of panel surface, the Sun provides $0.85\,\text{kJ}$ of energy in $1.0\,\text{s}$. The panels operate at $16\%$ efficiency. What power do they generate?

May/June 2021

A $100\,\text{W}$ lamp is left on for five hours each day over three weeks. Each unit of electricity costs $\$0.24$. What is the cost of using the lamp for this period?

May/June 2021

A $100\,\text{W}$ lamp is turned on for five hours each day over three weeks. The price of one unit of electricity is $\$0.24$. What is the cost of running the lamp for this period?

May/June 2021

A load is pulled by a rope connected to a motor. The resultant force applied by the rope to the load is shown in the diagrams. For every diagram, the load travels in the direction of the force shown and takes $10\,\text{s}$ to move $1.0\,\text{m}$. In which diagram does the motor do work at the greatest power?

May/June 2022

A $1000\,\text{W}$, $240\,\text{V}$ electrical device is turned on. What amount of energy does it use in $5.0\,\text{minutes}$?

May/June 2022

A rope connected to a motor pulls a load. The diagrams show the resultant force applied by the rope to the load. For every diagram, the load moves in the same direction as the force arrow and takes $10\,\text{s}$ to travel $1.0\,\text{m}$. In which diagram does the motor produce the greatest power?

May/June 2022

A microwave oven has a power consumption of $1500\,\text{W}$. One $1.0\,\text{kWh}$ of electrical energy costs $24$ cents. What is the cost of operating the microwave oven for $10$ minutes?

May/June 2023

What amount of energy, in kilowatt-hours, is consumed by a $1000\,\text{W}$ heater when it is connected to a $230\,\text{V}$ supply for $30$ minutes?

May/June 2024

What expression is used to calculate power?

Oct/Nov 2016

An electric motor is used to run a lift (elevator). The motor does $140\,000\,\text{J}$ of work in $70\,\text{s}$. Calculate the output power of the motor.

Oct/Nov 2016

A car covers a distance of $200\,\text{m}$ in $20\,\text{s}$. The car's engine exerts a driving force of $1000\,\text{N}$. What power output is produced by the engine?

Oct/Nov 2017

At a hydroelectric power station, $4.2 \times 10^5\,\text{kg}$ of water flows through the turbines each second. The turbines are positioned $50\,\text{m}$ below the surface of the reservoir. Take the gravitational field strength $g$ as $10\,\text{N kg}^{-1}$. If there are no energy losses, what is the power output of the power station?

Oct/Nov 2017

A student uses a newton meter to pull an object horizontally across a flat surface through a distance $d$ in a time of $t$. The reading on the newton meter is $F$. What quantity is represented by $(F \times d) / t$?

Oct/Nov 2019

A student works out the energy consumed by an electric heater. What equation is used to calculate the energy $E$ in kWh?

Oct/Nov 2020

What does the term power mean?

Oct/Nov 2020

Two $100\,\text{W}$ lamps are arranged in parallel across the mains supply, as shown. What amount of electrical energy is delivered by the mains when the switch remains closed for $36$ minutes?

Oct/Nov 2021

Electricity costs $9.0$ cents/ $\text{kW h}$. Boiling the water in a kettle requires $0.060$ hours and uses $1.2$ cents of electricity. What is the power rating of the kettle?

Oct/Nov 2021

What does the term unit of power mean?

Oct/Nov 2022

A small motor is rated at an input power of $10\,\text{W}$ and runs for $5.0\,\text{minutes}$. Determine the electrical energy supplied to the motor during this interval.

Oct/Nov 2023

A battery transfers $3000\,\text{J}$ of energy to a small $2.0\,\text{W}$ electric motor before the battery can no longer function. For how long does the motor remain switched on?

Oct/Nov 2023

A crane raises a heavy load at a constant rate. Which unit is appropriate for the output power of the crane’s motor?

Oct/Nov 2024

Four objects with different masses are raised through different distances over different time intervals. In which combination of mass, distance and time is the greatest power transferred?

Oct/Nov 2024

An object with mass $m$ is raised by a vertical distance $d$ in a time of $t$. Which equation is used to determine the power $P$ needed to lift the object?

Oct/Nov 2025