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Physics > P3 > Flashcards

P3 Flashcards

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1
Q

Average speed equation

A

Average speed = (initial velocity + final velocity)/2 (divided by)

Or in symbol form: (V+U)/2

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2
Q

What does the gradient represent on a distance-time graph?

A

Speed

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3
Q

What is the difference between speed and velocity?

A

Velocity is the speed in a direction, while the speed does not have a direction

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4
Q

What is the equation for acceleration?

A

Acceleration = change in speed/time

In symbols: acc’n (m/s^2) = (V - U)/T

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5
Q

What does the gradient represent in a speed-time graph?

A

The acceleration

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6
Q

What does the area represent in a speed-time graph

A

The distance travelled

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7
Q

What is Newton’s second law?

A

“Acceleration is produced when a force acts upon a mass. The greater the mass of the object, the greater the amount of force needed to accelerate it.”

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8
Q

What is force equal to (in terms of Newton’s second law)

A

Force (N) = mass (kg) x acceleration (m/s^2)

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9
Q

What is the stopping distance of a vehicle?

A

It is the total distance needed to stop the vehicle

The total stopping distance = thinking distance + braking distance

The thinking distance is the distance travelled in the time it takes for the driver to react and start braking

The braking distance is the distance travelled whilst braking before the vehicle comes to a halt

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10
Q

What factors can affect the thinking distance ?

A
  • Use of drugs or alcohol (including some prescription drugs)
  • Whether you’re tired or not
  • Distractions such as listening to music
  • Age (as you get older your reactions become slower)
  • Speed (as the car would travel further in that time you took to react)
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11
Q

What factors can affect the braking distance ?

A
  • Whether the brakes are worn (the more worn they are, the less force they can apply)
  • How much force is applied (too much can make the wheels lock, car skids)
  • Road conditions (e.g. if the road is icy there is less friction between the tyres and the road)
  • Brake quality (better brakes will stop the car quicker)
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12
Q

What is ‘work done’?

A

Work done is the transferring, or transforming of energy, e.g. lifting weights transfers energy from the person to the weights

Work done (J) = force (N) x direction moved in the direction of the force (m)

‘J’ stands for joules, unit of energy

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13
Q

What is power

A

Power is the work done in a given time

Power (W) = Work done (J)/ time

A watt (W) is the joules/second

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14
Q

For any frame of time (1 second for example) what is power equal to?

A

Power = force x speed

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15
Q

What would have a larger power output, a lorry or a car?

A

A lorry would, because it is significantly heavier, therefore it would require more work to be done in order to move it, and so a more powerful engine is required

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16
Q

What is kinetic energy?

  • what has kinetic energy?
  • what affects the size of an objects kinetic energy?
  • equation?
A
  • any moving object has kinetic energy due to its motion
  • the size of an object’s KE depends on the mass of the object and the speed at which it is travelling (greater mass requires more KE to move it, a higher speed would require more KE to increase the speed)
  • KE = 1/2 x mass x velocity^2 (squared)
17
Q

What factors affect the fuel consumption of a vehicle ?

A
  • Energy required to increase the KE of the car, depending on the mass of the car and it’s contents
  • Work done against resistive forces such as friction and air resistance. More streamlined cars would have lower fuel consumption
  • Speed and driving style of the driver. Rapid acceleration increases the amount of fuel used
  • Road conditions. Driving in heavy rain tends to lead to more fuel being consumed per mile
18
Q

Equation for momentum?

A

Momentum (kg m/s) = mass (kg) x velocity (m/s)

19
Q

What is the equation of force involving a change in momentum

A

When the momentum of an object changes, there is a force on the object:

Force = change in momentum / time

20
Q

What happens to the force of an object when a change in momentum happens in a short space of time ?

A

The force increases when the time taken for the momentum to change is slower. This also means the deceleration/acceleration of the object will be high, as acceleration = force/mass

21
Q

What, in terms of momentum, happens in a collision e.g. a car crash?

A

The change in momentum is very sudden as the car suddenly goes from having lots of momentum to a complete halt when colliding with something

The momentum is transferred to the object collided with and, in the case of the car, the driver also.

22
Q

Name and briefly explain (in momentum terms) some safety features in a car PROTECTING PASSENGERS IN A COLLISION.

A

Seatbelt- stretches, rather than holding a passenger rigid to increase the time at which the momentum changes, absorbs some of the shock.

Crumple zone- bends, absorbing some of the energy from the collision, less effect on the passenger(s)

Airbag- air filled cushion slows the passenger gently, ensuring they don’t hit the solid interior of the car with force

Collapsible steering column- bends, absorbing some of the energy of the collision. Also prevent the driver hitting it with a lot of force.

23
Q

Name and briefly explain some car features designed for ACCIDENT PREVENTION

A

Anti-lock braking system- stops wheels locking into a skid when too much force is applied by the breaks, wheels remain in contact with the road

Traction control- compensates for differences between the grip of the car’s four wheels e.g. If one wheel hits some ice, the traction control takes effect

Paddle controls- controls for various things found on or around the steering wheel so the driver doesn’t have to take their hands off the wheel (e.g radio, heating and even gear changing can be done by buttons/toggles on the steering wheel)

24
Q

In what ways do car safety features reduce the forces acting in a collision?

A
  • increasing the time taken for the passengers to stop, or the time taken for the collision to happen
  • increasing the stopping or collision distance
  • decreasing the acceleration of passengers
25
Q

How are new safety features for vehicles designed and tested?

A
  • data is gathered at real crash sites and analysed
  • scientists and engineers investigate accident cause and prevention
  • data from crash test dummies is used to analyse the benefits and risks of new safety features
26
Q

What is the equation for weight?

A

Weight (N) = mass (kg) x gravitational field strength (n/kg)

27
Q

What is the approximate gravitational field strength on earth ?

A

9.8 n/kg

28
Q

What happens to the air resistance/drag/friction as the speed of an object increases ?

A

It increases to balance the forces.

The force on the object remains the same, but the object is accelerating. The drag increases to match it. When the forces are balanced, the object stops accelerating.

29
Q

What happens, in terms of forces and speed, to a skydiver BEFORE they open their parachute?

A
  • when they first leave the airplane, the resultant force is only the downward one, weight
  • the person accelerates, but the downward force acting upon them remains the same. As they accelerate, the air resistance/friction increases

The friction increases until it matches the downward force, and the person no longer accelerates when this happens. They remain at a constant speed at this point, aka terminal velocity

30
Q

What happens, in terms of forces and speed, WHEN a skydiver OPENS their parachute?

A
  • the parachute creates more air resistance, making the resultant force upwards, therefore there is an acceleration upwards (and so the skydivers speed decreases).
  • as the speed downwards decreases, the air resistance also decreases
  • eventually, the air resistance and weight become balanced, so the skydiver reaches terminal velocity again, only it is much slower because of the parachute decreasing the speed
31
Q

How does the shape of an object affect drag?

A

The more streamline it is, the less drag it will have. This means the air is pushed to the sides or over the top of the object because of its shape

32
Q

How does the drag affect fuel consumption of a vehicle?

A

The more drag/frictional forces applied to the vehicle the more fuel it will have to consume to accelerate

More streamlined vehicles therefore consume less fuel

33
Q

What is the equation for gravitational potential energy ?

A

GPE (J) = mass (kg) x gravity (n/kg) x height (m)

34
Q

How does one increase the GPE of an object

A

By the object being higher up

35
Q

What is the link between GPE and KE of falling objects

A

As the object falls, the GPE converts into KE.

Not all of it though as some is lost to the surroundings.

36
Q

How can you calculate the height from which an object is dropped, given that:

Change in GPE (mgh) = change in kinetic energy (1/2mv^2)

Assuming we know the speed at which it fell

A

Mgh = 1/2mv^2 can be re-arranged to give h = (v^2)/2g

Physics (6 decks)

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