4 c) work and power

Question 1

4.9 know and use the relationship between work, force and distance moved in the direction of the force:

Answer 1

work=force x distance

W=F x d

Question 2

4.10 understand that work done is equal to energy transferred

Answer 2

Doing work means the energy is either decreased or increased. If a weight of 500N is raised 2m, 1000J of work is done. That means energy is increased by 1000J. Therefore work done is equal to energy transferred.

Question 3

4.11 know and use the relationship:

Answer 3

gravitional potential energy=mass x gravitional acceleration x height

G.P.E=mgh

Question 4

4.12 know and use the relationship:

Answer 4

Kinetic energy = ½ x mass x velocity2

K.E = ½ x m x v2

Question 5

4.13 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work

Answer 5

An object of mass, m weights mxg newtons. So the force, F, needed to lift is mg. If we raise the object through a distance h, the work done on the object is mgh. This is also the gain of GPE.

When the object is raised, it falls-it loses GPE but gains KE. At the end of the fall, all the initial GPE is converted into KE. And that’s how energy is conserved.

work done lifting object=gain in GPE=gain in KE of the object just before hitting the ground

Question 6

4.14 describe power as the rate of transfer of energy or the rate of doing work

Answer 6

Power is the rate of transferring energy or doing work. Its measures how fast energy is transferred.

Question 7

4.15 use the relationship between power, work done (energy transferred) and time taken:

Answer 7

power=(work done)/time

P=W/t