P10: Force and Motion

Question 1

What is Newton’s first law of motion?

Answer 1

If the resultant force on an object is zero and it is stationary, it will remain stationary, if it is moving, it will be moving at constant velocity

Question 2

What causes an object’s velocity to change?

Answer 2

A resultant force

Question 3

What is Newton’s second law of motion?

Answer 3

The acceleration of an object is proportional to the resultant force acting on the object and inversely proportional to the mass of the object

Question 4

How does acceleration change with force?

Answer 4

The greater the force applied, the greater the acceleration

Question 5

What is the formula for force in relation to acceleration?

Answer 5

F = ma
Force = mass * acceleration
(N) (Kg) (m/s²)

Question 6

What is inertia?

Answer 6

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

Question 7

What is inertial mass?

Answer 7

A measure of how difficult it is to change the velocity of an object.
force needed to accelerate : acceleration produced
- a large inertial mass requires a greater force to produce the same acceleration

Question 8

What is Newton’s third law?

Answer 8

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

Question 9

What are the forces acting on a skydiver?

Answer 9

They fall due to gravity, and experience a resultant force acting downwards because the force of gravity is more than that of air resistance. As they fall, they experience friction with air molecules, acting upwards, at a certain point, air resistance balances the weight of the skydiver and reach a resultant force of 0. (moving at constant velocity - terminal velocity)

Question 10

Why is a parachute nessesary for a skydiver?

Answer 10

Increases surface area to increase air resistance - air resistance is now greater than the weight - resultant force acting upwards, causing the skydiver to decelerate. Skydiver will fall at a lower terminal velocity, making it safe for them to hit the ground.

Question 11

What is stopping distance?

Answer 11

The total distance travelled from when the driver first spots the obstruction to when the car actually stops
Thinking distance + braking distance = stopping distance

Question 12

What is the thinking distance?

Answer 12

Distance travelled by the car during the driver’s reaction time

Question 13

What is the braking distance?

Answer 13

Distance travelled from when the driver applies the breaks to when the car actually stops

Question 14

How does the speed at which a vehicle is travelling at affect stopping distance?

Answer 14

Speed increases stopping distance

Question 15

What factors influence reaction time/ thinking distance?

Answer 15

Fatigue
Alcohol
Drugs
Other distractions

Question 16

What factors influence braking distance?

Answer 16

Icy road - reduces friction
Worn tyres - reduces friction
Worn brakes

Question 17

What happens during braking?

Answer 17

A brake presses against the wheel, a force of friction now acts between the brake and the wheel. The kinetic energy of the car is now converted to thermal energy in the brakes - causing a temperature increase
Car slows down as it loses kinetic energy.

Question 18

How does speed affect braking force?

Answer 18

Greater breaking force is required to stop a certain distance. This will cause rapid deceleration. Breaks can overheat

Question 19

What is momentum?

Answer 19

The product of mass and velocity. All moving objects have momentum, if it is stationary, its momentum is zero

Question 20

What is the formula for momentum?

Answer 20

Momentum = mass * velocity
(kg m/s) (kg) (m/s)

Question 21

What is the conservation of momentum?

Answer 21

In a closed system, total momentum before an event = total momentum after an event

Question 22

How do things like seatbelts and air bags protect you?

Answer 22

They increase the time taken for you to stop, therefore decrease the rate of change of momentum, meaning less force is applied.

Question 23

What is the formula for change in momentum?

Answer 23

Force (N) = (mass (kg) * change in velocity (m/s) / change in time (s)

Question 24

Why can rapid changes in momentum be fatal?

Answer 24

They result in a huge force being applied, which is dangerous. Risk can be reduced by making the change in momentum happen over a longer time