Work, energy and powerAQA A-Level Physics: Flashcards
What these 12 flashcards ask
- Write the equation for work done by a force at an angle to the motion.
- Define the joule.
- When does a force do no work?
- What does the area under a force-displacement graph represent?
- Define power.
- Define the watt.
- Write P in terms of force and velocity.
- State the equation for efficiency.
- A car at constant speed has resistive force 600 N at 25 m s⁻¹. What is the engine power at the wheels?
- What is the work done lifting a 5.0 kg object 2.0 m at constant speed? (g = 9.81 N kg⁻¹)
- Which component of the weight acts along a slope at angle θ?
- What happens to the energy that is not usefully transferred?
Exam questions on Work, energy and power
- A student pulls a suitcase across a level floor using a handle. The handle makes an angle of 30° above the horizontal and the force in the handle is a constant 40 N. The suitcase moves 25 m along the floor in 20 s.The student raises the handle so that it makes an angle of 60° above the horizontal, with the same force and distance. State and explain the effect on the work done.2 marks
- A car travels along a straight, level road at a constant speed of 25 m s⁻¹. The total resistive force on the car is 600 N. The engine's fuel supplies energy at the rate of 60 kW.Calculate the efficiency of the car's engine and drive system.2 marks
- A crate of mass 20 kg is at rest on a smooth horizontal floor. A horizontal force pushes the crate in a straight line. The force increases uniformly from 0 to 80 N over the first 5.0 m of the crate's motion, then stays constant at 80 N for a further 3.0 m. Friction is negligible.State the significance of the area under a force-displacement graph and calculate the work done on the crate in the first 5.0 m.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).