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Physics Unit 2 > Forces and Motion > Flashcards

Forces and Motion Flashcards

0
Q

What is acceleration?

A

Change in velocity per second

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1
Q

What are long vehicles fitted with to ensure they don’t drive too long?

A

A tachograph

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2
Q

What does the area under a velocity-time graph represent?

A

Distance

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3
Q

A force can change…?

A

The shape of an object or it’s state of motion

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4
Q

What force on a car makes it move?

A

The driving force (sometimes called the engine force or motive force). This is due to friction between the ground and the tyre on each drive wheel

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5
Q

What two forces are always acting on you?

A

Gravity and the force supporting you

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6
Q

What the resultant force on an object is zero…?

A

It will remain stationary if it was at rest or continue to move at the same velocity if it was already moving

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7
Q

Resultant force = mass x ?

A

Acceleration

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8
Q

For any car travelling at a constant velocity, the resultant force is?

A

Zero, because the force of the engine is balanced by the resistive forces (friction, air resistance and friction between parts of the car)

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9
Q

How does a driver vary the driving force or a vehicle?

A

Using the accelerator

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10
Q

The breaking force needed to stop a vehicle depends on…?

A

The speed of the vehicle when the brakes are first applied and the mass of the vehicle

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11
Q

Thinking distance is equal to?

A

Car speed x driver’s reaction time.

Stopping distance is equal to this plus braking distance.

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12
Q

Factors affecting stopping distance include?

A

Tiredness, alcohol, distractions, road conditions and the maintenance of the vehicle

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13
Q

The weight of an object is the force of gravity on it.

A

The mass (kg) is the quantity of matter

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14
Q

Gravitational field strength is measured in…?

A

N/kg.

Weight = mass x gfs

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15
Q

When we release an object above the ground, it falls because of it’s weight (force of gravity). If it has no other force acting on it, it’s weight is it’s resultant force. It accelerates downwards at a constant acceleration due to gravity. Air resistance is very small in a short descent so it is often ignored.

A

Yes.

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16
Q

If an objects falls in a fluid, the fluid drags on the object. The drag force increases with speed so the acceleration decreases as it falls and the resultant force decreases. It reaches terminal velocity when the resultant force is zero.

A

Yes.

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17
Q

Why is a squash ball elastic?

A

It regains it’s original shape

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18
Q

The extension of a steel spring is directly proportional to the weight hung on it. Who’s law is this?

A

Hooke’s Law

19
Q

A rubber band will not give a straight line, nor will a polythene strip because it stretches very little at first, the ‘gives’ and stretches easily.

A

Yes.

20
Q

When an object is stretched, which sort of energy is stored in it because work has been done on it?

A

Elastic potential energy

21
Q

If the force on a steel spring becomes too large, it will go beyond the limit of proportionality. Otherwise, the extension of the spring is directly proportional to the force applied to it. Any object that acts the same way obeys Hooke’s law. The rubber band and polythene strip have a very low limit of proportionality.

A

Yes.

22
Q

The stiffer a spring is, the greater the…?

A

Spring constant

23
Q

Reducing the speed of a vehicle will reduce the amount of fuel is uses. Why?

A

The resistance at high speed is much greater than that at low speed. Lorry drivers can fit a wind deflector over the can to reduce air resistance so less fuel is needed to maintain a certain speed

24
Q

Speed limits vary on the motorway according to what?

A

How much traffic there usually is

25
Q

If you are caught speeding, you can be fined or lose your licence. In some areas, residents are supplied with mobile speed cameras. Some say this is to increase the council’s income.

A

Yes.

26
Q

At traffic lights there are anti-skid surfaces with rougher surfaces. What is their purpose?

A

To increase friction between the surface and a vehicle tyre to reduce the chance of skidding when the driver applies the brakes

27
Q

Skidding happens when…?

A

Brakes are applied to harshly, causing the wheels to lock and the tyres to slide on the road

28
Q

When an object is moved by a force, we say what is done?

A

Work

29
Q

Energy transferred to an object = amount if work done. What does work done equal?

A

Force applied x distance moved in the direction of the force

30
Q

Most of the work done to overcome friction is transferred to which type of energy?

A

Heat

31
Q

When you lift something up, your muscles transfer chemical energy into…?

A

Gravitational potential energy

32
Q

Gravitational potential energy is energy stored in an object because if its position in the Earth’s gravitational field. When an object is moved up, the GPE…?

A

Increases

33
Q

Work done when an object moves up or down depends on…?

A

How far it is moved vertically and it’s weight

34
Q

Kinetic energy is equal to…?

A

1/2mv^2

35
Q

Kinetic energy recovery systems do what in a car?

A

Story kinetic energy when the vehicle brakes to use later on

36
Q

Hybrid cars use electric generators to transfer kinetic energy into electrical energy which is stored in the battery.

A

Yes.

37
Q

Elastic potential energy is the energy stored in an elastic objects when…?

A

Work is done to change its shape.Lots of this energy is turned into kinetic energy when the material regains its shape.

38
Q

Momentum is equal to…?

A

Mass x velocity

39
Q

If two trolleys of the same mass crash together, the velocity of trolley A is halved by the impact and the combined mass is twice that as before the collision. So momentum stays the same. This applies to any closed system (where no resultant forces are acting). The total momentum before an event is equal to the total momentum after an event.

A

Yes.

40
Q

If two single trolleys travel equal distances in the same time they recoil at equal speeds when they collide.

If a double trolley only travels half the speed of a single trolley, the speed is half that of the single trolley. In both occasions, momentum is the same and they recoil in opposite directions.

A

Yes.

41
Q

The total momentum before and after an explosion is…?

A

The same

42
Q

An artillery gun of mass 2000kg fires a shell of mass 20kg at a velocity of 120m/s. What is the recoil velocity of the gun?

A

20 x 120 = 2000 x ?
2400 = 2000 x 1.2
Recoil velocity = 1.2m/s

43
Q

What are crumple zones at the front and rear ends of a car designed to do?

A

Lessen the force of an impact. READ NOTES ON THIS.

44
Q

A seatbelt acts across the chest. What is the purpose of this?

A

To spread out the force of a collision

45
Q

In a crash, cars have air bags which inflate to spread out the force of an impact across the upper part of the body which increases the impact time so the effect of the force is lessened.

A

Yes.

46
Q

Why do some car manufacturers not like having extra safety features on their cars?

A

They are expensive to produce

Physics Unit 2 (4 decks)

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