Energy, Power and Work Done

What is work done?

The amount of energy transferred when an external force causes an object to move over a certain distance.

What is the unit for work done?

Joule (or Nm, 1Nm=1J)

What is the equation for work done if the force applied is parallel to the direction of the object's displacement?

W=Fs W=work done(J) F=force(N) s=displacement(m)

What is the equation for work done if the force applied is at an angle to the objects displacement?

W=Fscos(theta)

How does the equation W=Fscos(theta) change regarding motion?

horizontal motion= cos(theta)

vertical motion=sin(theta)

How do you know what component (horizontal or vertical) of a force is needed when calculating work done?

The component needed is the one parallel to the displacement.

Where is theta located when calculating work done?

The angle between the force and direction of displacement.

When is work done a maximum and minimum?

Maximum- when theta= 0 degrees

Minimum- when theta= 90 degrees

What is the base unit for Joules regarding work done

Kg m^2 s^-2 (W= mascos(theta))

What is power

The rate of doing work or the rate of energy transfer.

What is the equation for power?

change in work done/ change in time

What does the equation power= change in work done/ change in time show?

Power is increased if there is a greater energy transfer or energy is transferred over a shorter amount of time.

If an object is moving at a constant velocity with a constant force what is the equation for power?

P=Fv F=force(N) v=velocity(ms^-1)

What is the requirement for the equation P=Fv?

The force must be in the direction of the velocity, otherwise the component of the force in the direction of the velocity must be used instead.

What is the unit of power?

Watts (W)

How can work done be found using a graph?

The area under a force-displacement graph.

What is a non constant force called?

A variable force.

How do you find work done if the force is varying?

The equations P=Fv and W=Fd can't be used so you must find the area under a force-displacement graph.