P10 - Forces in motion

Question 1

What is the equation that links acceleration, change in velocity and time taken?

Answer 1

Acceleration = change in velocity/time taken

Question 2

Newton’s first law

Answer 2

If the resultant force acting on an object is zero and
- the object is stationary, the object remains stationary
- the object is moving, the object continues to move at thesame speed and in the same direction. So the object continues to move at the same velocity

Question 3

What is inertia?

Answer 3

• Tendency of the objects to continue in their state of rest or of uniform motion

Question 4

Newton’s second law

Answer 4

• 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 5

What is the equation that links acceleration, mass and resultant force?

Answer 5

Resultant force = mass * acceleration

Question 6

What is inertial mass?

Answer 6

• The ration of force over acceleration
• inertial mass is a measure of how difficult it is to change the velocity of an object

Question 7

What is the symbol for an approximate value?

Answer 7

≈

Question 8

Newton’s third law

Answer 8

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

Question 9

What is stopping distance?

Answer 9

The sum of the thinking distance and braking distance

Question 10

What is thinking distance?

Answer 10

The distance a vehicle travels during the driver’s reaction time

Question 11

What is braking distance?

Answer 11

The distance a vehicle travels under a braking force to stop

Question 12

What is the typical reaction time of a person?

Answer 12

0.2 and 0.9 seconds

Question 13

What can a driver’s reaction time be affected by?

Answer 13

• Tiredness
• Drugs
• Alcohol
• Distractions

Question 14

What are examples of adverse road conditions?

Answer 14

Wet or icy conditions

Question 15

Explain a method to test human reaction times

Answer 15

1. Line up ruler
2. Drop the ruler
3. Measure the distance
4. Use acceleration due to gravity
   Find change in velocity

Question 16

What are examples of poor vehicle condition?

Answer 16

Poor conditions of the brakes and tyres

Question 17

What happens when a force is applied to the breaks?

Answer 17

• Work is done by the friction force between the brakes and the wheel to reduce kinetic energy of the vehicle. - The temperature of the brakes increases

Question 18

What happens the greater the braking force? What do large decelerations lead to?

Answer 18

• The greater the deceleration of the vehicle
• Large decelerations can lead to brakes overheating and loss of control, risk of injuries of passengers

Question 19

What is the equation linking mass, momentum and velocity?

Answer 19

momentum=mass * velocity

Question 20

What is the unit for momentum?

Answer 20

Kilograms metre per second (kg m/s)

Question 21

What is the conservation of momentum?

Answer 21

In a closed system, the total momentum before an event is equal to the total momentum after the event

Question 22

Explain examples of momentum during a collision of two skaters

Answer 22

1. When colliding both skaters will move with a lower velocity
2. Total momentum before and after the collision remains constant
3. The momentum transferred from skater B to skater A results in both skaters moving together

Question 23

Explain examples of momentum during a collision of a car and a stationary van

Answer 23

1. When a car collides with a stationary van, the car’s momentum is transferred to the van, causing it to move forward
2. Total momentum of the car and the van is the same before and after the collision

Question 24

Explain examples of momentum during a collision of a ball on a wall

Answer 24

1. When a ball hits a wall, it exerts a force on the wall and the wall exerts an equal and opposite force back on the ball
2. The ball changes its direction and velocity, resulting in a change in momentum

Question 25

Describe what can affect the stopping distance of a lorry

Answer 25

1. The overall stopping distance is a combination of thinking distance and braking distance 2. Factors affecting thinking distance: tiredness of the driver, how distracted the driver is, alcohol, medication causing tiredness 3. Factors affecting braking distance: condition of lorry, worn tyres and brakes braking distance will increase. Road conditions as wet and icy, there will be reduced friction which can increase braking distance. Speed and mass of the lorry affects braking distance as if it is heavy and travelling fast then the braking distance will be higher

Question 26

When does a change in momentum occur?

Answer 26

When a force acts on an object that is moving, or able to move

Question 27

What is the equation for change in momentum?

Answer 27

change in momentum over change in time equals force F=m∆v/∆t

Question 28

What two equations are linked involving acceleration?

Answer 28

F=m * a a=v-u/t

Question 29

Explain how an airbag works

Answer 29

It increases the time it takes for a person’s head to decelerate during a collision and so this reduces the force they experience, they rapidly inflate and provide a cushion-like surface

Question 30

Explain how a seat belt works

Answer 30

- It increases the time over which a passenger’s momentum changes during a crash - reducing the force experienced by the passenger, the belt is stretched slightly which prevents the passenger from hitting a hard surface - spreads the impact force over a large area and longer time

Question 31

Explain how a gym crash mat works

Answer 31

- A gymnast will sink into the mat slightly because they are compressible and take a longer time to come to a stop - they increase the time taken to come to a stop - decrease the rate of change of momentum and decrease in force - Reduces the force of impact

Question 32

Explain how a cycle helmet works

Answer 32

- Has a layer of foam which acts as a compressible layer -reducing the force of impact - increase the time taken to come to a stop

Question 33

Explain how a cushioned surface in playgrounds work

Answer 33

- They are compressible so if a child falls over, they will take longer to completely stop moving - the surface increases time taken to come to a stop

Question 34

Explain how a cushioned surface in playgrounds work

Answer 34

- Compressible so if a child falls over, they will take longer to completely stop moving - Surface increases time time taken to come to a stop