CP2 Forces and Motion

Question 1

Resultant force

Answer 1

The sum of all forces acting on an object

Question 2

What does it mean if an object has a resultant force of 0N ?

Answer 2

The forces are balanced
The object is moving at a constant velocity, or is at rest

Question 3

What is the resultant force of an object traveling at a constant velocity?

Answer 3

0N

Question 4

What does it mean if the resultant force is not 0N ?

Answer 4

The object can either be accelerating, decelerating, or changing direction

Question 5

Weight

Answer 5

The force acting upon an object due to gravitational attraction

Question 6

Where does the force of gravity on Earth always pull to?

Answer 6

The centre of the Earth

Question 7

The effect of the force of gravity in an object is called the object’s ….

Answer 7

Weight

Question 8

What are forces measured in?

Answer 8

Newtons (N)

Question 9

Mass

Answer 9

The mass of an object is the amount of matter an object is made from

Question 10

What is mass measured in?

Answer 10

Kilograms (kg)

Question 11

What is weight measured in?

Answer 11

Newtons (N)

Question 12

How can we calculate the weight of an object?

Answer 12

Weight = Mass * Gravitational Field Strength

Question 13

What’s the gravitational field strength of Earth (to the nearest while number) ?

Answer 13

10N/kg

Question 14

What’s the weight of a 5kg mass on Earth’s surface?

Answer 14

5kg * 10N/kg = 50 N

Question 15

What piece of equipment can be used to measure the weight of an object?

Answer 15

Newton metre or Force metre

Question 16

How does an object move if the forces acting on it are balanced? (two answers)

Answer 16

The object stays at rest, or moves at a constant velocity

Question 17

Calculate the weight of an object when the mass is 50kg, and the gravitational field strength is 1.6N/kg.

Answer 17

50 kg * 1.6 N/kg = 80 N

Question 18

Acceleration

Answer 18

A measure of how much an object’s velocity changes in a certain amount of time

Question 19

How do you calculate acceleration?

Answer 19

Acceleration = change in velocity / time
a = (v-u) / t

Question 20

Name the two factors that affect acceleration

Answer 20

• the size of the force
• the mass of the object

Question 21

What’s the equation that states the relationship between force, mass, and acceleration?

Answer 21

Force = mass * acceleration
f = m * a

Question 22

What is acceleration measured in?

Answer 22

m/s^2

Question 23

What force will make a mass of 4kg accelerate at 5 m/s^2 ?

Answer 23

Force = 4 * 5 = 20 N

Question 24

A force of 50N acts on a 2kg mass. What will be the acceleration of the mass?

Answer 24

Acceleration = 50/2 = 25 m/s^2

Question 25

A force of 2000N accelerates a car at 2.5 m/s^2. What is the mass of the car?

Answer 25

Mass = 2000/2.5 = 800 kg

Question 26

Newton’s First Law

Answer 26

“An object at rest stays at rest, and an object in motion stays at a constant speed and in a straight line unless acted upon by force.”

Question 27

Newton’s Second Law

Answer 27

“The acceleration of a moving object depends upon its mass and the force acting on it.”

Question 28

Newton’s Third Law

Answer 28

“If one object exerts a force on another object, then the other object exerts an equal and opposite force on the first object.”

Question 29

The acceleration of an object is : (proportionality..)

Answer 29

- Directly proportional to the resultant force on the object - Inversely proportional to the mass of the object

Question 30

What does directly proportional mean?

Answer 30

If two things are directly proportional, they increase and decrease together

Question 31

What does inversely proportional mean?

Answer 31

If A is inversely proportional to B, this means that as A increases, B will decrease by the same factor

Question 32

Inertial mass

Answer 32

A measure of how difficult it is to change the velocity of an object (the ratio of force over acceleration)

Question 33

How are Action-Reaction forces different to Balanced forces?

Answer 33

Action-reaction forces act of different objects, whereas balanced forces act on the same object

Question 34

How are Action-Reaction forces similar to Balanced forces?

Answer 34

The forces are equal in size, and act in opposite directions

Question 35

For two forces to satisfy Newton’s third law, they need to:

Answer 35

- Act on different objects - Be equal in magnitude - Act in opposite directions - Be the same type of force

Question 36

Momentum

Answer 36

A measure of the tendency of an object to keep moving, or how hard it is to stop moving

Question 37

What two things does the momentum of an object depend on?

Answer 37

The object’s mass and velocity

Question 38

How can momentum be calculated?

Answer 38

Momentum = mass * velocity p = mv

Question 39

A 500 kg wrecking ball is moving at 10 m/s when it hits a building. What is its momentum?

Answer 39

500 * 10 = 5,000 kg m/s

Question 40

What is momentum measured in?

Answer 40

kg m/s

Question 41

A 500 kg wrecking ball has a momentum of 1500 kg m/s. What is its velocity?

Answer 41

1500 / 500 = 3 m/s

Question 42

A football is kicked at a velocity of 6 m/s. It has a momentum of 240 kg m/s. What is its mass?

Answer 42

240/6 = 40 kg

Question 43

Why does a motorcycle travelling at 30 m/s have less momentum than a car travelling at the same speed?

Answer 43

Momentum depends on mass as well as velocity - a motorcycle usually has a smaller mass than a car, so will have less momentum than a car at the same velocity.

Question 44

Conservation of Momentum

Answer 44

When moving objects collide, the total momentum of both objects is the same before the collision as it is after the collision - if there are no external forces.

Question 45

Which formula expressed the relationship between momentum, force, and time

Answer 45

Force = change in momentum / time F = (mv-mu) / t

Question 46

A car has a mass of 2000kg. Its velocity changes from 5 m/s to 10 m/s in 5 seconds. What force causes this change in velocity?

Answer 46

F = (20,000 - 10,000) / 5 = 2,000 N

Question 47

A toy car has a mass of 2 kg. Its velocity changes from 2m/s to 5m/s, with a force of 4N. How long does this change in velocity take?

Answer 47

t = ((2kg * 5m/s) - (2kg*2m/s)) / 4N = 1.5 s

Question 48

How do you calculate stopping distance?

Answer 48

Stopping distance = thinking distance + braking distance

Question 49

Stopping distance

Answer 49

The total distance a car travels until it stops

Question 50

Thinking Distance

Answer 50

The distance the car travels between the driver seeing a danger and them acting upon it

Question 51

Braking Distance

Answer 51

The distance a car travels until it stops, once the brakes have been applied

Question 52

Name some factors that affect thinking distance

Answer 52

- Tiredness - Distractions - Alcohol - Drugs

Question 53

Name some factors that affect braking distance

Answer 53

- Weather - Condition of the car’s tyres or brakes - Road conditions - Speed of the car

Question 54

A car travels 7m during a driver’s reaction time, then a further 23m whilst the car is braking. What was the car’s stopping distance?

Answer 54

7m + 23m = 30 m

Question 55

A car travels 46m whilst the car is braking. The total stopping distance was 56m. What was the driver’s thinking distance?

Answer 55

56m - 46m = 10 m

Question 56

Name three safety features a car has to reduce force in a collision

Answer 56

- Seat belts - Air bag - Crumple zone

Question 57

Velocity

Answer 57

The speed of an object in a given direction

Question 58

What happens to an objects velocity if they are moving in a circular path, and why?

Answer 58

Its velocity is always changing. The speed might be constant, but the direction is always changing so therefore the velocity changes too.

Question 59

What do we call the resultant force acting on an object travelling in a circular path?

Answer 59

The Centripetal Force

Question 60

Equilibrium

Answer 60

When a situation is not changing because all the things that affect it balance out