State the formula for work done by a torque on a rotating object.

W = Tθ, where W is work done, T is torque, and θ is angular displacement.

In the equation W = Tθ, what does the symbol θ represent and what unit must it be measured in?

θ represents angular displacement and must be measured in radians.

Calculate the work done when torque = 393 N m, angular displacement = 18.7 rad.

Work done = 393 × 18.7 = 7350 J.

State the equation for power transmitted by a rotating shaft.

P = Tω, where P is power, T is torque, and ω is angular velocity.

In the formula P = Tω, what quantity does ω represent and what is its SI unit?

ω represents angular velocity, measured in rad s⁻¹.

AQA A-Level Physics 7408

Measurements and Their Errors

Topic overview Use of SI units and their prefixes Limitation of physical measurements Estimation of physical quantities

Particles and Radiation

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Medical PhysicsOptional topic

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Engineering Physics

Work and power

3 things to know
Paper 3, section B

Overview

Work done by a torque, power transmitted by a rotating shaft, and the effect of friction.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

How is work done by a torque calculated, and what unit does it take?

Numbers

How is power transmitted by a rotating shaft calculated, and what reduces useful output?

Key term

Where does frictional torque typically arise in rotating machinery?

Questions from this subtopic

Each one with the model answer underneath.

1
State the formula for work done by a torque on a rotating object.
Model answer
W = Tθ, where W is work done, T is torque, and θ is angular displacement.
2
In the equation W = Tθ, what does the symbol θ represent and what unit must it be measured in?
Model answer
θ represents angular displacement and must be measured in radians.
3
What is the SI unit of work done by a torque?
Model answer
Joules (J).
4
Calculate the work done when torque = 393 N m, angular displacement = 18.7 rad.
Model answer
Work done = 393 × 18.7 = 7350 J.
5
State the equation for power transmitted by a rotating shaft.
Model answer
P = Tω, where P is power, T is torque, and ω is angular velocity.
6
In the formula P = Tω, what quantity does ω represent and what is its SI unit?
Model answer
ω represents angular velocity, measured in rad s⁻¹.

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