Module 3 - Chapter 5 - Work, energy and power Flashcards
What is the equation for work done?
W = Fx
work done = force x distance moved in the direction of the force
What is the unit for work done?
Nm or Joule (J)
How much work would be done on a 10kg block if it was being held stationary in mid air, 1.5m above the ground?
0J because the block has not moved so no work has been done
Does work done = energy transferred
Yes, all energy from work done will be transferred to other stores useful and waste
What is the equation for work done at an angle?
W = Fxcosθ
Or sine rule
What is the law of conservation of energy?
Energy cannot be created or destroyed only transferred
Is it possible to achieve perpetual motion?
Not with current capabilities since with what humans can achieve there will always be an external force or waste energy in some form in any system
Name 5 forms of energy
> Kinetic energy
Gravitational potential energy
Chemical energy
Elastic potential energy
Electrical potential energy
Nuclear energy
Radiant (electromagnetic energy)
Sound energy
Internal / thermal energy
State the formula for kinetic energy
Ek = ½mv²
kinetic energy = half x mass x velocity²
Derive the equation for kinetic energy
W = Fs F= ma
W= mas
_
v² = u² + 2as
u² = 0
v² = 2as
as = v²/2
_
W = m x v²/2
Ek = W
∵ Ek = ½mv²
State what gravitational potential energy is
Gravitational potential energy is the capacity for doing work as a result of an objects position in a gravitational field
State the equation for GPE
In a uniform gravitational field:
Ep = mgh
GPE = mass x gravitational field strength x height
_
Ep is also equivalent to work done
_
grav. field strength on earth is 9.81 for A-level physics
What happens to an objects KE and GPE as it falls?
As an object falls, its GPE decreases and its KE increases due to GPE being transferred to KE
Use an equation to link GPE and KE
Due to principle of conservation of energy:
KE = GPE
mgh = ½mv²
mass cancels out so :
gh = ½v²
What is power?
Power is the rate at which work is done
