Factual Recall

Question 1

What is the difference between mass and weight?

Answer 1

Mass is how much “stuff” there is.

Weight is the force of gravity on an object.

Question 2

What is an object’s centre of mass?

Answer 2

The position on an object where the weight acts from.

Question 3

Explain why the object moves at constant speed.

Answer 3

• The first force is equal to the second force on the object.
  o For example, for terminal velocity, the weight is equal to the drag on the object.
• Therefore, the NET FORCE is zero.
• Due to Newton’s First Law, this means the acceleration of the object is zero.

Question 4

Define thinking distance

Answer 4

The distance travelled by a driver from when the driver sees the problem and the brakes are applied.

Question 5

Define braking distance

Answer 5

The distance travelled by the car after the brakes are applied until the car stops.

Question 6

State the name of the force opposing the motion of the truck/diver/whatever it is.

Answer 6

Drag

Question 7

State Hooke’s Law

Answer 7

The extension is directly proportional to the force applied, as long as the elastic limit is not exceeded.

Question 8

State the principle of moments

Answer 8

When an object is in equilibrium, the sum of the clockwise moments equals the sum of the anticlockwise moments.

Question 9

What does a force extension graph look like for a perfect spring?

Answer 9

Straight line through the origin

Question 10

What does a force extension graph look like for a metal wire?

Answer 10

Straight line through the origin that curves down after a short while.

Question 11

What does a force extension graph look like for a rubber band?

Answer 11

An “s” shape that is NOT a straight line that is lower on the way down to the way up.

Question 12

Explain how a falling object reaches terminal velocity.

Answer 12

• There is a net force downwards.
• So it accelerates downwards because of F = ma.
• There is a force of drag upwards.
• Drag increases as speed increases…
• …until the drag force is equal to the speed.
• Then, the net force is zero…
• …so it moves at constant speed, due to Newton’s First Law.

Question 13

Taking into account air resistance, what happens to the sky diver’s velocity over time.

Answer 13

• There is a net force downwards.
• So it accelerates downwards because of F = ma.
• There is a force of drag upwards.
• Drag increases as speed increases…
• …until the drag force is equal to the speed.
• Then, the net force is zero…
• …so it moves at constant speed, due to Newton’s First Law.