P2.2

Question 1

Newton’s first law

Answer 1

An object will continue to stay at rest or move with uniform velocity unless acted upon by a resultant force.
- Takes a resultant force to change the motion of an object.
- Inertia is a measure of how difficult it is to change an object’s velocity.

Question 2

Newton’s second law

Answer 2

The acceleration experienced by a body is directly proportional to the resultant force acting upon it, and in the same direction as.
- F = ma
- a = v-u/t

Question 3

Newton’s third law

Answer 3

For every action there is an equal and opposite reaction.

Question 4

Terminal velocity

Answer 4

The velocity at which a body falls through a medium, when the drag acting on the body is equal to its weight.

Question 5

Explain why terminal velocity is a constant speed

Answer 5

At terminal velocity the weight of a body is balanced by the drag force acting on it. Therefore, the resultant force is zero, and so the body does not accelerate.

Question 6

Momentum - elastic vs inelastic

Answer 6

Momentum = mass x velocity P = m x V
- Momentum of a system is always conserved. Total momentum before an event is equal to that after the event.
- Elastic collision = All ke is returned so no energy is transferred to other stores.
- Inelastic collision = Not all ke is returned so some energy is transferred to other stores.

Question 7

Work and power

Answer 7

Work is the transfer of energy when a force acts on an object.
W = F x d
Power is the rate of energy transfer.
P = W/t

Question 8

How do you explain the motion of falling objects?

Answer 8

When you jump out of a plane you accelerate. Your motion changes because there is a resultant force on you. The air exerts a force on you, but the Earth exerts a larger force. As you accelerate the force of the air increases. Eventually the force of the air on you equals the force of the Earth on you, and your motion no longer changes. You have reached terminal velocity. A parachute increases the force of the air to reduce your velocity.

Question 9

Why do objects move in a circle?

Answer 9

An object moving in a circle at a constant speed is constantly changing direction. Thus, it is constantly changing velocity. This means it is constantly accelerating, and so must be subject to a resultant force, known as a centripetal force. The centripetal force always acts towards the centre of the circle and acts only to change the direction of the the velocity.