# P2.3

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What happens when work is done moving an object?
When a force moves an object - supplied energy is transferred to the object so work done = energy transferred.
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What is the equation for work done?
W (work done (J) = F(Force(N) × d (distance moved in the direction of the force(m)
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How do you know if no work is done?
If the distance moved is zero.
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Which force is work done to overcome?
Friction-mainly transferred into energy by heating i.e. when brakes are applied in a car the friction between the wheel discs + brake pads oppose motion of the wheel. Kinetic energythermal energy
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What is gravitational potential energy?
Energy stored in an object because of its position in the Earth’s gravitational field. When object is moved vertically GPE = work done (by lifting force)
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What is the equation for Gravitational Potential force?
E = mgh. Change in GPE (J) = mass (kg) × Gravitational field strength (N/kg) × change in Height (m)
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What is power and how can it be calculated?
Rate of energy transfer. P = E ÷ t. Power (W) = Energy (J) ÷ time (s)
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What does the kinetic energy of a moving object depend on?
Greater mass + faster the speed, the more kinetic energy the objects has.
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What is the equation for Kinetic energy?
Ek = ½ × m × v2. Kinetic Energy (J) = ½ × Mass (kg) × speed (m/s)
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What is elastic potential energy?
How energy transferred when work is done on an elastic object to stretch/squash it is stored.
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What makes an object elastic?
When it regains its shape after being stretched/squashed.
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How is momentum affected and how can it be calculated?
The greater the mass + velocity the greater the momentum. P = m × v. momentum (kgm/s) = mass (kg) × velocity (m/s)
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What is the law of conservation of momentum?
Whenever objects interact, the total momentum before the interaction is equal to the total momentum afterwards (provided no external forces act on them).
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Objects at rest are at zero momentum. Why is the total momentum after an explosion zero?
In an explosion the objects move apart with equal + opposite momentum. 1 momentum is positive & the other negative so total momentum is 0 after the explosion i.e. bullet = gun recoils.
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Why are side impact bars and crumple zones built into cars?
They fold up in a collision to increase the impact time and reduce the forces acting.
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Why are seat belts and air bags built into cars?
As they spread the forces on the body across a larger area so that when the drivers head hits the airbag it changes the momentum slowly and seatbelt increases the impact time reducing the force.
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## Other cards in this set

### Card 2

#### Front

What is the equation for work done?

#### Back

W (work done (J) = F(Force(N) × d (distance moved in the direction of the force(m)

### Card 3

#### Front

How do you know if no work is done?

### Card 4

#### Front

Which force is work done to overcome?

### Card 5

#### Front

What is gravitational potential energy?