Forces and motion Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

Does a distance quantity require a specific direction?

A

No specific direction is required so it is a scalar quantity?

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

If an object moves 3 meters to the left and then 3 meters back to its initial position, what is the object’s total displacement?

A
  • The object has 0 displacement.
  • Displacement is a vector quantity so it also involves direction.
  • The object starts and ends at the same point.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

State a typical value for the speed of sound

A

330 m/s.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the typical value for walking speed?

A

1.5 m/s.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is a typical value for human running speed?

A

3 m/s.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is a typical value for human cycling speed?

A

6 m/s.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

State the equation linking distance, speed and time. Give appropriate units

A

Distance = speed x time

Distance (m), speed (m/s), time (s).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Why can an object travelling at a constant speed in a circle not have a constant velocity?

A
  • Speed is a scalar quantity.
  • Velocity is a vector quantity which means it can only be constant if the direction is constant.
  • In circular motion, the direction is continuously changing.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How can speed be calculated from a distance-time graph?

A

The speed is equal to the gradient of the graph.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What must be done to calculate speed at a given time from a distance-time graph for an accelerating object?

A
  • Drawing a tangent to the curve at the required time.

- Calculating the gradient of the tangent.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

State the equation for the average acceleration of an object. Give appropriate units

A

Acceleration = (change in velocity) / (time taken)

Acceleration (m/s²), velocity (m/s), time (s).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How can distance travelled by an object be calculated from a velocity-time graph?

A

It is equal to the area under the graph.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Give an approximate value for the acceleration of an object in free fall under gravity near the earth’s surface

A

9.8 m/s².

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What can be said about the resultant force acting on an object when it is falling at terminal velocity

A
  • The resultant force is zero.

- When at terminal velocity, the object is moving at constant speed and so isn’t accelerating.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

State newton’s first law for a stationary object

A

If the resultant force on a stationary object is zero, the object will remain at rest.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

State newton’s first law for a moving object

A

If the resultant force on a moving object is zero, the object will remain at constant velocity (same speed in the same direction).

17
Q

What can be said about the braking forces and driving forces when a car is travelling at constant velocity?

A

The braking forces are equal to the driving forces.

18
Q

If an object changes direction but remains at a constant speed, is there a resultant force?

A

Since there is a change in direction, there is a change in velocity and so there must be a resultant force.

19
Q

What is inertia?

A

The tendency of an object to continue in its state of rest or uniform motion.

20
Q

State the defining equation for newton’s second law

A

Resultant force = mass x acceleration

F = m a

21
Q

State newton’s second law in words

A

An object’s acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass.

22
Q

What is inertial mass?

A
  • A measure of how difficult it is to change a given object’s velocity.
  • The ration of force over acceleration.
23
Q

What is the symbol used to represent an approximate value?

A

~

24
Q

State newton’s third law

A

Whenever 2 objects interact, the forces they exert on each other are always equal and opposite.

25
Q

What is the stopping distance of a vehicle equal to?

A

The sum of thinking distance and braking distance.

26
Q

For a given braking distance, if the vehicle’s speed is increased, what can be said about its stopping distance?

A

The stopping distance is increased with an increase in speed.

27
Q

Give a typical range of values for human reaction time

A

0.2 seconds - 0.9 seconds.

28
Q

Give 3 factors which can affect a driver’s reaction time

A
  • Tiredness.
  • Drugs.
  • Alcohol.
29
Q

Give factors which may affect braking distance

A
  • Wet, icy road conditions.
  • Poor tyre/brake conditions.
  • Higher mass (more KE).
  • Higher velocity (more KE).
30
Q

Describe the energy transfers that take place when a car applies its brakes

A
  • Work is done by the friction force between the brakes and wheel.
  • Kinetic energy of the wheel is converted to heat and is dissipated to the surroundings through the brake discs.
31
Q

To stop a car in a given distance, if its velocity is increased, what must happen to the braking force applied?

A

The braking force must also be increased.

32
Q

State 2 consequences of a vehicle undergoing very large decelerations

A
  • Kinetic energy converted to heat is very high causing brakes to overheat.
  • Loss of control of the vehicle.