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GCSE Physics > Topic 5d - Momentum and Car Safety > Flashcards

Topic 5d - Momentum and Car Safety Flashcards

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1
Q

What is momentum?

A

Momentum = mass x velocity

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2
Q

What is the equation for momentum?

A

p = mv

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3
Q

What is the unit for momentum?

A

kg m/s
OR
Ns

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4
Q

What kind of quantity is momentum?

A

A vector quantity => direction is important. (usually left and right direction).

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5
Q

What is impulse?

A

The change in momentum of an object.

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6
Q

What is the unit for impulse / change in momentum?

A

kg m/s
OR
Ns

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7
Q

What is the equation for impulse?

A

change in p = m (v-u)

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8
Q

What must you ensure to do when calculating an impulse problem?

A

State the directions you are choosing to use (which way you put the + and -)

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9
Q

What is a force in relation to momentum?

A

A force is the change in momentum per unit time/ the rate of change of momentum.

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10
Q

What is the equation for Force in relation to momentum?

A

F = change in p / t
OR
change in P = F t

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11
Q

What kind of force is the force used in F = change in p / t?

A

An average force.

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12
Q

What is the principle of conservation of momentum?

A

Total final momentum of the system (after) = Total initial momentum of the system (before)

Provided there are no external forces acting.

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13
Q

In what 2 situations is the principle of conservation of momentum applicable?

A
  • Collisions (when objects join)
  • Explosions (when objects move apart)
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14
Q

How can propulsion be explained using the example of a balloon? (4)

A
  • Air filled balloon = before. The total momentum of the air + balloon = 0.
  • When clamp released, air is ejected at high speed from the neck of the balloon.
  • Air at high speed has momentum to the left, so the balloon has the same momentum to the right.
  • Releasing the air makes the balloon move at speed in opposite direction to the air due to the principle of conservation of momentum.
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15
Q

What is true about all collisions?

A

They conserve momentum.

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16
Q

What do the types of collisions depend on?

A

The total kinetic energy.

17
Q

What does it mean if a collision is elastic?

A

Total kinetic energy of the system before = Total kinetic energy of the system after.

18
Q

What does it mean if a collision is inelastic?

A

Total KE before =/ (NOT) Total KE after

19
Q

What happens to objects in inelastic collisions?

A

One or more of the objects get deformed.

20
Q

What is the definition of stopping distance?

A

The total distance travelled during the time it takes for a car to stop in response to some emergency.

21
Q

What is the equation for stopping distance?

A

Stopping distance = Thinking distance + Braking distance

22
Q

What is an emergency stop?

A

Where maximum force is applied by the brakes to stop car in shortest possible distance.

23
Q

What is thinking distance?

A

The distance travelled by a car from when the driver realises they need to break, to when they apply the brakes.

24
Q

What is braking distance?

A

The distance travelled under the braking force.

25
Q

How would you describe the relation / proportionality between braking force, speed and stopping distance?

A

For a given braking force, the greater the speed of the vehicle, the greater the stopping distance.

26
Q

What is the definition of reaction time?

A

A measure of how much time passes between seeing something and reacting to it.

27
Q

What is the human reaction time for an alert person?

A

Usually in range of 0.2 - 0.9 seconds

28
Q

What are the 5 steps to the reaction time test with a ruler?

A
  1. Person A holds a 30cm ruler vertically, such that the bottom end of the ruler hovers over the top of the hand of Person B.
  2. Person A should release the ruler unexpectedly.
  3. As soon as Person B sees the ruler move, they should close their hand, catching it.
  4. The ruler is marked at the point which it was caught by Person B => in line with top of hand.
  5. This gives a measurement of the distance the ruler feel => greater distance, longer reaction time.
29
Q

What is the equation for reaction distance?

A

Reaction distance = Speed of the car x Driver’s reaction time

30
Q

What 2 things affect the thinking distance?

A
  • Speed
  • Reaction time
31
Q

What 5 factors is braking distance affected by?

A
  • Speed
  • Condition of brakes
  • Condition of tyres => minimum tread of depth 1.6 mm
  • How good the grip is
  • Load of the vehicle (mass/ weight)
32
Q

How do tread patterns help tyres in wet conditions?

A

In wet conditions tread patterns help to stop water getting trapped between the tyres and the road => provides a channel through which the water can ‘escape’.

33
Q

What will happen if a vehicle has too little tread?

A

Tyres may lose contact with the ground, causing vehicle to slide.

34
Q

What are 4 factors that affect reaction time?

A
  • Distractions
  • State of mind => intoxication
  • Tiredness
  • Age (not best one)
35
Q

How does a car slow down when brakes are applied? (4)

A
  • When brakes applied, there is a frictional force between brakes and wheels of car.
  • This frictional force does work on brakes => transfers energy from car to brakes.
  • So KE of car decreases, and thermal energy of brakes increases.
  • Means car decelerates.
36
Q

What could a large deceleration lead to?

A

To the brakes overheating and / or loss of control of the vehicle.

37
Q

What is the equation for work done by the brakes?

A

Braking force x Breaking distance = 1/2 x Mass x Velocity squared

GCSE Physics (8 decks)

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