P1P2 - Motions and Forces

Question 1

What is Newtons 1st Law?

Answer 1

An object will stay stationary or at a constant velocity and direction unless acted upon by an external force

Question 2

What is Newtons 2nd Law?

Answer 2

Resultant force (F) = mass (m) x acceleration (a).
F = ma

Question 3

What is Newtons 3rd Law?

Answer 3

Every action has an equal and opposite reaction

Question 4

What is a resultant force?

Answer 4

The resultant force is the sum of all the forces acting on the object.

Question 5

What is the equation for resultant force?

Answer 5

Resultant force = Mass x Acceleration
F = ma

Question 6

What is the equation for finding momentum?
What is the equation for finding change in momentum?

Answer 6

Momentum = Mass x Velocity
P = mv

Change in momentum = Force x Time
*P = Fv

Question 7

What is the law of conservation of momentum?

Answer 7

The law of conservation of momentum says that momentum cannot be created or destroyed.

So, if two objects collide, the sum of momentum before collision = sum of momentum after collision.

Question 8

What are the units for Momentum?

Answer 8

Kgm/s

Question 9

What is the equation for Acceleration?

Answer 9

Acceleration = change in velocity / time taken

Question 10

What are some safety features of an object with high momentum? EG Car - Why are they efficient?

Answer 10

• Seat belts, air bags and crumple zones that absorb the kinetic energy transferred by collisions.
• They increase the time taken for the change in momentum to happen, reducing the forces involved.

Question 11

How is a rocket launched in terms of momentum?

Answer 11

• 1 The rocket starts at rest and has no momentum.
• 2 The rocket pushes the fuel out of the bottom of the rocket. The fuel has gained momentum in the direction of the ground (earth).
• 3 The conservation of momentum means that the rest of the rocket must gain momentum in the opposite direction. This propels (pushes) the rocket into the sky.

Question 12

What is meant by Inertia?

Answer 12

How difficult it is to change the object’s motion.
This is called inertia.
An object with a high mass has more inertia than an object with a lower mass.

Question 13

What is the equation for Weight?

Answer 13

Weight = Mass x Gravitational field strength
W = mg

Question 14

What is weight?

Answer 14

The force acting downwards on an object due to gravity.

Question 15

What is circular motion?

Answer 15

An object moving in a circle at a constant speed (circular motion).

It’s constantly changing direction and velocity. The resultant force always acts towards the centre of the circle and the object is always accelerating.

This resultant force towards the centre of the circle is called the centripetal force.

Question 16

What is stopping distance? Example?

Answer 16

Stopping distance is the distance it takes a car to stop in an emergency (i.e. when the car is braking suddenly).

Question 17

How do you calculate stopping distance?

Answer 17

Stopping distance = thinking distance + braking distance

Question 18

What factors affect stopping distance?

Answer 18

• Tiredness
• Drugs or alcohol
• Distractions

Question 19

What factors would affect braking distance?

Answer 19

• Initial car speed
• Condition of car
• Road conditions

Question 20

How can we measure human reaction times?

Answer 20

Ruler drop test

Question 21

What is a humans typical reaction time?

Answer 21

0.25s

Question 22

How do you convert km/h into m/s ?
EG : 1.8km/s

Answer 22

1. Convert km into m
   1.8km X 1000 = 1800m
2. Convert hours into seconds
   60 × 60s = 3600s
3. Divide metres by seconds
   1800⁄3600 m/s = 0.5m/s

Question 23

What happens if theres no resultant force acting on an object?

Answer 23

A moving object will continue in a straight line at a constant velocity.

Question 24

What is force equal to?

Answer 24

The rate of change of momentum.

Question 25

What’s the equation for force?

Answer 25

Change in momentum / time

Question 26

How do safety features in a car reduce the force felt by a person in a crash?

Answer 26

Safety features of a car increase the time taken for the momentum to change.
Therefore reducing the force felt by the person in the crash.

Question 27

What is the force experienced by a person whose momentum changes by 10kgm/s in 2s?

Answer 27

5N

Question 28

What are examples of a contact force?

Answer 28

Friction, air resistance, tension and normal contact force

Question 29

What are examples of a non-contact force?

Answer 29

Gravitational force, electrostatic force and magnetic force

Question 30

What is it called when the resultant forces are 0N?

Answer 30

Equilibrium

Question 31

What are the units for gravitational field strength?

Answer 31

N/kg

Question 32

What is the value of the earth’s gravitational field strength?

Answer 32

9.81N/kg

Question 33

What is the definition of weight?

Answer 33

The force acting downwards on an object due to gravity

Question 34

What is centripetal force?

Answer 34

A force that acts towards a centre

Question 35

Why are large decelerations dangerous?

Answer 35

A larger deceleration will transfer more stopping force to passengers. This harms passengers.

Question 36

What’s a typical reaction time for a human?

Answer 36

0.25s

Question 37

What is mass?

Answer 37

The mass of an object is a measure of the amount of matter it contains.

Question 38

Why is air resistance a frictional force?

Answer 38

Because it opposes the motion of objects moving quickly through air.