Work Done and Power

Work Done
and Power

Engineering Principles

Dropdown

At first you may be a little confused about the difference between work done and power.

Put simply, ​

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is the energy used when a force moves an object, while​

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is the rate at which work is done over time.

Multiple Choice

What is the SI Unit of Work Done?

• Joules (J)

• Newtons (N)

• Watt (W)

• Pascals (Pa)

Multiple Choice

What is the SI Unit of Power?

• Joules (J)

• Newtons (N)

• Watt (W)

• Pascals (Pa)

Multiple Choice

What is the SI Symbol for Work Done?

• p

• P

• W

• w

Multiple Choice

What is the SI Symbol for Power?

• p

• P

• W

• w

Equations: Work Done

1 J of work done results when 1 N of force is applied to move an object 1 m:

​Where:

• W is the work done (in Joules [J])

• F is the force applied (in Newtons [N])

• s is displacement (in metres [m])

​Equations: Work Done

You are expected to be able to rearrange the equation for Work Done to find Force or Displacement:

Equations

A power of 1 W results from 1 J of work done per second:

​Where:

• P is the power (in Watts [W])

• W is the work done (in Joules [J])

• t is the time (in seconds [s])

​Equations: Power

You are expected to be able to rearrange the equation for Power to find Work Done or Time:

Work Done Equation - Practice Questions

Multiple Choice

A vehicle is propelled 25,000 m by a force of 2000 N. Calculate the work done by the vehicle.

• 50 J

• 50 kJ

• 50 GJ

• 50 MJ

Multiple Choice

The work done by a vehicle travelling 8 km is 7.6 MJ. Calculate the force required to do this.

• 0.95 N

• 950 N

• 950 kN

• 950 MN

Multiple Choice

The work done by a vehicle is 3.75 MJ. If the force applied on the vehicle is 1.5 kN, calculate the displacement of the vehicle.

• 2500 m

• 2500 km

• 0.4 km

• 400 m

Math Response

A force of 15 N is used to push a box along the floor a distance of 3 m.  How much work was done?

[Your answer will be in Joules]

Type answer here

Correct Answer: 45

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Rad

Math Response

The force at the point of a shaping machine tool when it is cutting 2,400 N. If the length of the stroke is 18 mm, calculate the work done in one cutting stroke.

[Your answer will be in Joules]

Type answer here

Correct Answer: 43.2

Deg^°

Rad

Power Equation - Practice Questions

Multiple Choice

10 kJ of work is done by a force in moving a body uniformly through a distance in 50 s. Calculate the power.

• 125 W

• 150 W

• 175 W

• 200 W

Multiple Choice

The power used to lift an object using an elevator is 825 W. If the lift took 1 minute to lift the object, calculate the work done.

• 49.5 kJ

• 495 kJ

• 4950 kJ

• 49500 kJ

Multiple Choice

How much time is needed to produce 720 J of work if 90 W of power is used? 

• 0.125 s
• 8 s
• 125 s

• 80 s

Math Response

A blender performs 2000 J of work in 12.5 seconds. What is its power?

[Your answer will be in Watts]

Type answer here

Correct Answer: 160

Deg^°

Rad

Math Response

An engine reaches its top speed from rest in 7.5 s. It is able to perform 220,522 J of work in that time.  How much power does this engine have in that time? 

[Your answer will be in Watts, and you will need to state your answer to 2 d.p.]

Type answer here

Correct Answer: 29402.93

Deg^°

Rad

Practice Questions involving both Power and Work Done Equations

Math Response

A 100 N force is applied to move an object a horizontal distance of 5 meters at constant speed in 10 seconds. How much power is used?

[Your answer will be in Watts]

Type answer here

Correct Answer: 50

Deg^°

Rad

Math Response

A robot travels 45 m carrying a force of 1.5 kN in 20 s. Calculate the power used.

[Your answer will be in Watts]

Type answer here

Correct Answer: 3375

Deg^°

Rad

Math Response

A force of 3.5 kN is used to propel a vehicle for 25 s during a test drive. The power used by the vehicle is 105 kW. Determine the distance that the vehicle travels during the test drive.

[Your answer will be in metres]

Type answer here

Correct Answer: 750

Deg^°

Rad

Math Response

An industrial piston moves a mass of 250 kg at an acceleration of 8 ms^-2. Determine the power required if the stroke of 1.2 m is completed in 5.0 s.

[Your answer will be in Watts]

Type answer here

Correct Answer: 480

Deg^°

Rad

Math Response

An object with a mass of 40 kg is pulled by a cart so it moves 5 m/s in 2 seconds. Calculate the power used by the cart.

[Your answer will be in Watts]

Type answer here

Correct Answer: 500

Deg^°

Rad