Forces and Motion

Question 1

What do you do to the uncertainties when two quantities are multiplied/divided?

Answer 1

Add the percentage uncertainties.

Question 2

What do you do to the uncertainties when two quantities are added/subtracted?

Answer 2

Add the raw uncertainties.

Question 3

Fully describe how a falling object reaches terminal velocity.

Answer 3

🔸initially the only force acting on the object is its weight, which acts downwards. The resultant force >0 and the object accelerates downwards.
🔸As the object accelerated it hits more and more particles and therefore the drag increases, the resultant forces decreases and therefore the acceleration decreases.
🔸eventually the drag=Weight, the resultant force equals zero and the object stops accelerating. At this point the object moves at a constant speed, a terminal velocity.

Question 4

State the principle of moments

Answer 4

At equilibrium the sum of the clockwise moments = the sum of the anti-clockwise moments.

Question 5

What is Newton’s second law of motion?

Answer 5

The rate of change of momentum of an object is directly proportional to the resultant force acting on it ➡️ f=ma

Question 6

What is Newton’s first law?

Answer 6

If there is no resultant force acting on an object then it will remain in its state (either at rest or moving at a constant speed) unless external forces act.

Question 7

Explain why the values for the average speed and average velocity are different.

Answer 7

Speed is the rate of change of distance and is a scalar quantity that doesn’t take into account direction. Velocity is the rate of change of displacement and is a vector quantity that does take into account direction as well as magnitude.

Question 8

What are the two conditions for equilibrium?

Answer 8

1) no net force

2) no total moment

Question 9

What is Newton’s third law?

Answer 9

To every action there is an equal and opposite reaction force.

Question 10

True or false:

change in momentum = impulse

Answer 10

True
F= change in momentum/change in time
And
Impulse = F x change in time

Question 11

How do you find impulse from a force-time graph?

Answer 11

Area under the graph

Question 12

How do you find the distance travelled on a v-t graph?

Answer 12

Area under the graph

Question 13

What do you do to the uncertainties when two quantities are multiplied/divided?

Answer 13

Add the percentage uncertainties.

Question 14

What do you do to the uncertainties when two quantities are added/subtracted?

Answer 14

Add the raw uncertainties.

Question 15

Fully describe how a falling object reaches terminal velocity.

Answer 15

🔸initially the only force acting on the object is its weight, which acts downwards. The resultant force >0 and the object accelerates downwards.
🔸As the object accelerated it hits more and more particles and therefore the drag increases, the resultant forces decreases and therefore the acceleration decreases.
🔸eventually the drag=Weight, the resultant force equals zero and the object stops accelerating. At this point the object moves at a constant speed, a terminal velocity.

Question 16

State the principle of moments

Answer 16

At equilibrium the sum of the clockwise moments = the sum of the anti-clockwise moments.

Question 17

What is Newton’s second law of motion?

Answer 17

The rate of change of momentum of an object is directly proportional to the resultant force acting on it ➡️ f=ma

Question 18

What is Newton’s first law?

Answer 18

If there is no resultant force acting on an object then it will remain in its state (either at rest or moving at a constant speed) unless external forces act.

Question 19

Explain why the values for the average speed and average velocity are different.

Answer 19

Speed is the rate of change of distance and is a scalar quantity that doesn’t take into account direction. Velocity is the rate of change of displacement and is a vector quantity that does take into account direction as well as magnitude.

Question 20

What are the two conditions for equilibrium?

Answer 20

1) no net force

2) no total moment

Question 21

What is Newton’s third law?

Answer 21

To every action there is an equal and opposite reaction force.

Question 22

True or false:

change in momentum = impulse

Answer 22

True
F= change in momentum/change in time
And
Impulse = F x change in time

Question 23

How do you find impulse from a force-time graph?

Answer 23

Area under the graph

Question 24

How do you find the distance travelled on a v-t graph?

Answer 24

Area under the graph

Question 25

Is the moment of a force a vector or scalar quantity?

Answer 25

VECTOR

Question 26

Define the term ‘impulse’

Answer 26

Impulse acting on a body = change in momentum of the body
OR
Impulse of a force = magnitude of force x time it acts for

Question 27

True or false:

The force of drag is directly proportional to the square of the velocity of the falling body

Answer 27

True

Question 28

The trapdoor experiment to find the acceleration due to free fall is performed. The value of g found was greater than the true value. Give 2 reasons why.

Answer 28

• air resistance was not taken into account when calculating g.
• there may have been residual magnetism on the magnet so the ball wasn’t released at the right time.

Question 29

A ball bearing is dropped through a tube of a viscous liquid to determine the terminal velocity.
What would be the effect of changing the size of the ball bearing?

Answer 29

A smaller ball bearing - would reach terminal velocity more quickly and the terminal velocity would be lower.

A larger ball bearing - would take longer to reach terminal velocity and the terminal velocity would be higher.