Chapter 10 Force And Motion

Question 1

10.1 Resultant force equation

Answer 1

Mass x acceleration

Question 2

10.1 What is inertia?

Answer 2

It changes the velocity of an object. The tendency of an object to stay at rest or to continue in uniform motion.

Question 3

10.1 What happens to the resultant force if the velocity of an object is increasing?

Answer 3

The resultant force is at the same direction as the velocity.

Question 4

10.1 What happens to the resultant force if the object’s velocity is decreasing?

Answer 4

The resultant force is the opposite direction to its velocity.

Question 5

10.1 Newton’s second law of motion

Answer 5

The acceleration of an object is inversly proportional to the mass of an object.

Question 6

10.6 How does the impact time reduce the impact force?

Answer 6

The longer the impact time, the more the impact force is reduced.

Question 7

10.6 Impact force equation

Answer 7

Mass x change of velocity/ time taken

Question 8

10.4 Momentum equation

Answer 8

Momentum = mass x velocity

Question 9

10.4 What happens in a closed system in momentum?

Answer 9

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

Question 10

10.5 Conservation of momentum equation

Answer 10

(mass of A x velocity A) + (mass of B x mass of velocity B) = 0

Question 11

10.8 Force applied in a spring equation

Answer 11

Force applied = Spring constant x extension

Question 12

10.2 What is the weight of an object?

Answer 12

The force acting on an object due to gravity

Question 13

10.2 What is the mass of an object?

Answer 13

It depends on the quantity of matter in an object.

Question 14

10.2 What is the equation of weight

Answer 14

Mass x gravitational field strength

Question 15

10.2 What is the terminal velocity of an object?

Answer 15

The velocity it eventually reaches when it is falling. The weight of the object is then equal to the frictional force on the object.

Question 16

10.2 How does an object reach terminal velocity?

Answer 16

1. The acceleration of the object decreases as it falls. This is because the frictional force increases as it speeds up. So the resultant force on it decreases and therefore its acceleration decreases
2. The object reaches a constant velocity when the frictional force on it is eqaul and opposite to its weight. This velocity is called its terminal velocity. The resultant force is then zero, so its acceleration is zero.

Question 17

10.3 What does the braking force depend on?

Answer 17

• The speed of the vehicle when the brakes are first applied.
• The mass of the vehicle

Question 18

10.3 What happens to the decelaration when the speed increases?

Answer 18

The greater the speed, the greater the deceleration

Question 19

10.3 The greater the mass, what happens to the braking force?

Answer 19

The greater the mass, the greater the braking force

Question 20

10.3 What is the thinking distance?

Answer 20

The distance travelled by the vehicle in the time it takes the driver to react. Formula is speed x reaction time.

Question 21

10.3 What is the braking distance?

Answer 21

The distance travelled by the vehicle during the time the braking force acts.

Question 22

10.3 What factors affect the braking distance?

Answer 22

High speed
Poor weather conditions
Poor vehicle maintenance

Question 23

10.4 What factors increase the thinking distance

Answer 23

Tiredness
Alcohol
Drugs
Use of a mobile phone

Question 24

10.4 What happens to the momentum in a closed system

Answer 24

The total momentum before an event is equal to the total momentum after the event. You can use this in calculations when objects collide

Question 25

10.5 What is the formula of the conservation of momentum?

Answer 25

1. (Mass of A x velocity of A) + (mass of B x velocity of B) =0 So... 2. (Mass of A x velocity of A) = - (Mass of B x velocity B)

Question 26

10.5 In momentum, what happens when two objects push each other apart?

Answer 26

They move with different speeds if they have unequal masses, and with equal and opposite momentum, so their total momentum is zero.

Question 27

10.5 What happens when MaVa + MbVb =0

Answer 27

The two objects (A and B) recoil from each other.

Question 28

10.6 What happens when two vehicles collide

Answer 28

- They exert equal and opposite forces on each other. | - Their total momentum is unchanged.

Question 29

10.6 Explain the impact force equation

Answer 29

- Impact force = change of momentum / impact time | - So the shorter the impact time, the greater the impact force.

Question 30

10.6 How does a soft pad in front of a trolley reduce the impact force?

Answer 30

- A soft pad on the front of the trolley acts as a cushion to increase the impact time. - The momentum of the trolley would be reduced over a longer time, and so the change of momentum per second would be less. - Impact force is equal to the change of momentum per second, the impact force would be less.

Question 31

10.7 Why are cycle helmets and cushioned surfaces used?

Answer 31

These reduce imoact forces by increasing the impact time.

Question 32

10.7 Why are seat belts and air bags used?

Answer 32

They spread the force across the chest and increase the impact time.

Question 33

10.7 Why are side impact bars and crumple zones used?

Answer 33

They give way in an impact, and so increase the impact time.

Question 34

10.7 How can the conservation of momentum be used?

Answer 34

They can be used to find the speed of a car before an impact.

Question 35

10.8 What does it mean when an object is elastic?

Answer 35

An object is elastic if it returns to its original shape after removing the force deforming it.

Question 36

10.8 What is the extension of an object

Answer 36

The difference between the length of the object and its original length. Extension = Length at the stage - original strength

Question 37

10.8 What is the relationship between the extension and force applied?

Answer 37

The extension of a spring is directly proportional to the force applied to it, as long as the limit of proportionality is not exceeded. This relationship is linear.

Question 38

10.8 What happens beyond the limit of proportionality?

Answer 38

The extension of a spring is no longer proportional to the applied force. This relationship becomes non-linear.