Motion, forces and energy - energy

what is energy

- it is the ability to do work

what is the SI Unit of energy

joules (J)

What are some of the types of energy

> mechanical energy
> thermal/heat energy
> sound energy
> light energy
> chemical energy
> electrical energy etc.

mechanical energy can be split into

> kinetic energy
> potential energy

potential energy can be split into

> gravitational potential energy
> elastic potential energy

what is gravitational potential energy (g.p.e)

- is the energy possessed by a body due to its position above the ground

what are the factors of g.p.e

⬆weight ⬆g.p.e
⬆height ⬆g.p.e

formulaes for g.p.e

g.p.e = weight x height (w x h)
g.p.e = mass x gravitational pull x height (m x g x h

QUESTIONS on g.p.e

-

1. An object with a mass of 15kg is at a point above the ground of 10m. Calculate the g.p.e

g.p.e = m x g x h
= 15 x 10 x 10
= 1500J

2. An object held at a point above the ground has 2352 J of g.p.e. The objects mass is 20kg. How far above is the object from the ground

g.p.e = m x g x h
h = g.p.e ÷ (m x g)
= 2352 ÷ (20 x 10)
= 2352 ÷ 200
= 11.76m

3. An object held at a point 1.5m has 1200J of g.p.e. Calculate the mass of the object.

g.p.e = m x g x h
m = g.p.e ÷ (h x g)
= 1200 ÷ (1.5 x 10)
= 1200 ÷ 15
= 80kg

4. An athlete of mass 50kg runs up a hill of height 1200m above sea level. The foot of thehill is 400m above sea level. How much did g.p.e increase

g.p.e = m x g x h
h = 1200 - 400
= 800

g.p.e = m x g x h
= 50 x 10 x 800
= 400,000J

what is kinetic energy

- is the energy possessed by moving objects

what are the factors of k.e

⬆mass ⬆k.e
⬆speed ⬆k.e

formulae for k.e

k.e = 1/2 of mass x speed²
= 1/2mv²

NOTE

k.e is a scalar quantity (only affected by size and magnitude)