Module 3 Work, Energy and Power

Question 1

Define Work done.

Answer 1

Work done by a force is the product of the force applied and the distance moved in the direction of the force by an object. Work done is equal to energy transferred.

Question 2

Define the unit joule.

Answer 2

It is the energy transferred when 1 newton of force moves an object by 1 meter in the direction of the force.

Question 3

How to find work done if the force is at an angle to the direction of the motion.

Answer 3

Use the formulae F x s x cosTheta

Question 4

State the principle of conservation of energy. Define any terms you use.

Answer 4

In a closed system, a system where all the energy transfers are accounted for and no energy or matter enters or exits the system. The principle of conservation of energy states that no energy can be created or destroyed, only transferred from one form to another.

Question 5

How do you calculate elastic energy?

Answer 5

Using 1/2 x F x e, where F is magnitude of force applied and e is the extension.

Question 6

Derive the equation for kinetic energy.

Answer 6

Ek=Work done = F x s
F = ma
W.d = mas
v^2=u^2 +2as
v^2-u^2/2s=a

W.d = m x (v^2-u^2/2s) x s
K.E= m x(v^2-u^2/2) = 1/2 m v^2 (as we can assume initial velocity is zero)

Question 7

Derive equation for gravitational potential energy.

Answer 7

G.p.e = W.d = F x s
F = Weight of body
F = mg
s = h ( height moved vertically)
G.p.e = mgh

Question 8

Derive the equation of Power of an object in motion.

Answer 8

P=E/t
E= W.d
W.d= F x s
P=F s/t
s/t= v
P = F v