P2.2 - Newtons Laws

Question 1

What is a force?

Answer 1

A push or pull acting on an object due to an interaction with another object.

Question 2

What are the two categories that all forces can be split into?

Answer 2

1. Contact forces (objects touching)

2. Non-contact forces (objects separated)

Question 3

Give three examples of contact forces.

Answer 3

1. Friction
2. Air resistance
3. Tension

Question 4

Give three examples of non-contact forces.

Answer 4

1. Gravitational forces
2. Electrostatic forces
3. Magnetic forces

Question 5

What is the name given to the single force that is
equivalent to all the other forces acting on a given
object?

Answer 5

The resultant force.

Question 6

State Newton’s first law for a stationary object

Answer 6

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

Question 7

State Newton’s first law for a moving object.

Answer 7

If the resultant force on a moving object is zero, the object will remain at constant velocity

Question 8

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

Answer 8

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

Question 9

When does an object fall with terminal speed?

Answer 9

● When the upwards forces (air resistance) and the downwards forces (weight) are equal to each other
● No resultant force, so constant speed

Question 10

What happens to the magnitude of air resistance on

a falling object when the velocity increases?

Answer 10

As velocity increases, the force of air resistance on the object will also increase.

Question 11

State the defining equation for Newton’s Second

Law

Answer 11

Resultant force (N) = Mass (kg) x Acceleration (m/s²)

F = ma

Question 12

State Newton’s Second Law in words.

Answer 12

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

Question 13

What is inertia?

Answer 13

inertia is an object’s resistance to motion

Question 14

What is inertial mass?

Answer 14

● A measure of how difficult it is to change a given object’s velocity.
● The ratio of force over acceleration.

Question 15

State Newton’s Third Law.

Answer 15

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

Question 16

State the equation used to calculate an object’s

momentum.

Answer 16

Momentum (kgm/s) = Mass (kg) x Velocity (m/s)

P = mv

Question 17

What is the unit used for momentum?

Answer 17

kgm/s

Kilogram metres per seconds

Question 18

State an equation linking change in momentum,

force and time.

Answer 18

Force x Time = Change in Momentum
F Δt = P
F Δt = mΔv

Question 19

What quantity is equal to the force experienced in a

collision?

Answer 19

The rate of change of momentum

Question 20

What does it mean if a force is said to do ‘work’?

Answer 20

The force causes an object to be displaced through a distance.

Question 21

What is the equation used to calculate work done? Give appropriate units.

Answer 21

Work done = Force x Distance
W = Fd
Work done (Joules), Force (Newtons), Distance (metres)

Question 22

Under what circumstance is 1 joule of work done?

Answer 22

When a force of 1 Newton causes a displacement of 1 metre

Question 23

What is power?

Answer 23

The rate at which work is done.

Question 24

State the equation used to calculate power. Give

appropriate units.

Answer 24

Power (W) = Work Done (J) / Time (s)