Work And Power Flashcards
What is the work done?
The work done is the amount of energy transferred, whenever a resultant force moves a body in the direction of the force.
How do forces transfer energy?
Mechanically
What does a force overcome?
An opposing force (eg. friction or air resistance)
Calculating work done
More energy is transferred if the force is increased, as the object moves a greater distance.
Work done formula
Work done (J) = Force (N) x Distance (m)
How do you lift an object?
To lift an object, you must apply a minimum force that equals (balances) the weight.
Weight formula
Weight (N) = mass (kg) x gravitational field strength (N/kg)
Gravitational field strength on Earth
~9.8 N/kg
Gravitational acceleration on Earth
~9.8 m/s^2
What is a powerful person scientifically?
In the scientific sense of transferring energy, a powerful person or device can do a lot of work in a short space of time.
What is power?
Power is the amount of energy transferred each second (or the rate of energy transferred).
Power formula
Power (W) = Energy Transferred (J) / Time (s) = Work Done / Time
P = E/T or W/T
What is the unit of power?
Watts (W), where W is the number of Joules (J) transferred per second
Electric cooker
As you change the controls on an electric cooker, the electrical power of the heating element changes. The higher the power, the hotter the ring gets. This is because more energy is bering transferred by electric current into thermal energy of the ring each second.
Car power
The most powerful car transfers more chemical energy (in the fuel) into kinetic energy per second. This means it can accelerate more rapidly to a higher speed.
Power of an energy saving light bulb
20W
Power of a normal light bulb
100W
Power of a human
100W
Power of a horse
736W
Power of a kettle
3kW
Power of a power station
850MW
Gravitational Field Strength
The gravitational field strength at Earth’s surface produces a force of approximately 10N for every 1kg of mass. On heavier planets, like Jupiter, gravity is greater. Hence, the gravitational potential energy gained would also be greater for the same change in height.
GPE formula
Change in GPE (J) = mass (kg) x gravitational field strength (N/kg) x change in height above ground (m)
ΔE = mgΔh
However, sometimes, there is no GPE.
What is 1GJ?
1 billion J
What is 1kJ?
1 thousand J
What is kinetic energy?
Kinetic energy is the energy stored in an object’s movement.
What is kinetic energy?
Kinetic energy is the energy stored in an object’s movement.
Kinetic energy formula
Kinetic energy (J) = 1/2 x mass (kg) x velocity^2 (m/s)
E(k) = 1/2(m)(v^2)
m = 2E(k) / v^2
v = root(2E(k) / m)
