P10 Force and Motion

Question 1

What is hooke’s law?

Answer 1

The extension of a spring is directly proportional to the force used to strech the spring

This dosen’t apply to weight after it’s limit of proportionality

Question 2

How to find the spring constant?

Answer 2

Spring Constant = Force / Extenstion
K=F/e

Question 3

How to find elastic potential energy?

Answer 3

Elastic Potential Energy = 1/2 x Spring Constant x extension^2
or
Elastic Potential Energy = 1/2 x Force x extension

Question 4

What is elastic potential energy measured in?

Answer 4

Joules

Question 5

How to find the force applied to a spring?

Answer 5

Force = Spring Constant x Extension

Question 6

What are elastic objects?

Answer 6

Objects that can go back to it’s orginal shape when force is released

Question 7

What are plastic objects?

Answer 7

Objects that cannot go back to its original shape after being compressed or stretched even after releasing the force.

Question 8

How to perform the hooke’s law experiment?

Answer 8

1) Place the weight holder only on the spring and note the position of the pin against the metre rule.

2) Add 1N (100g) to the holder and note the new position of the pin

3) Calculate the extension of the spring

4) Repeat stages 1-3 for 2N,3N,4N and 5N. However don’t exceed 6N

Question 9

What is the gravitational field strength of the Earth?

Answer 9

9.8 N/Kg

Can be rounded to 10N/Kg

Question 10

What are the effects of an unbalanced force?

Answer 10

• A stationary object will start to move towards the resultant force
• If the resultant force is acting upon the same direction the object is moving then it’ll accelerate
• When the resultant is acting upon the opposite direction the object is moving then it’ll start to deccelerate then eventually stop

Question 11

What is terminal velocity?

Answer 11

Maximum constant velocity an object can achieve when in travels in a fluid.

Question 12

Describe the terminal velocity of a man oppening his parachute.

Answer 12

1. At the start of his jump the air resistance is smaller than the weight so he accelerates downward
2. As the divers velocity increases his air resistance will increase
3. Eventually the air resistance will be big enough to equal the sky diver’s weight reaching the first terminal velocity
4. When the diver opens his parachute the air resistance suddenly increases, causing him to slow down
5. Because he is slowing down his air resistance will increase again until it balances his weight.
6. The sky diver has now reached a new,lower terminal velocity

Question 13

Air resistance is affected by two factors :

Answer 13

• Surface area of the object
• Velocity of the object

Question 14

What is the equation for work done?

Answer 14

Work done (joules) = Force (Newtons) x Distance (Metres)

Question 15

What is the resultant force for a car at constant velocity?

Answer 15

0

Question 16

An accelerator pedal is used to……

Answer 16

vary the driving force of the engine.

Question 17

What does the breaking force in a given distance depend on?

Answer 17

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

Question 18

How to find resultant force?

Answer 18

Resultant force = mass x acceleration

Question 19

How to find the impact force?

Answer 19

Force = (Mass x Change in Velocity) / time taken

Question 20

The longer the impact time……

Answer 20

the more the impact force is reduced

Question 21

What is momentum?

Answer 21

The tendency of the object to keep moving in the same direction

Question 22

What is the equation for momentum?

Answer 22

Momentum = Mass x Velocity
Kg m/s = Kg x m/s
p = m x v

Question 23

What is a closed system?

Answer 23

• A physical system that doesn’t exchange matter of energy with it’s surroundings
• It is when the total momentum before an event is equal to the total momentum after the event

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Question 24

Opposing forces to driving force:

Answer 24

Air resistance and Friction

Question 25

Is momentumn a scaler or vector quanitiy?

Answer 25

Vector

Question 26

What is inertia?

Answer 26

The tendancy of an object to stay at rest or in uniform motion.

Question 27

What forces oppose the driving force in a car?

Answer 27

Friction and Air resistance

Question 28

What does the stopping distance of a car depend on?

Answer 28

Thinking distance and Braking distance.

Question 29

What are factors which increase breaking distance?

Answer 29

• High speed
• Poor weather
• Poor vehicle maintanence

Question 30

What are factors which increase thinking distance?

Answer 30

Poor reaction time due to :
- tiredness
- alcohol
- drugs
- mobile phones

Question 31

What is the unit of momentum?

Answer 31

Kg m/s

Question 32

What is the equation for conservation of momentum?

Answer 32

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

Question 33

How do you calculate impact force?

Answer 33

Impact force = change of momentum / impact time