Chapter 7 Laws of motion and momentum

Question 1

What is newtons first law?

Answer 1

An object will remain at rest or continue moving with a constant velocity until acted on by an external force

Question 2

What is newtons third law?

Answer 2

When two objects interact, they exert equal and opposite force on each other.

Question 3

What are the 4 fundamental forces?

Answer 3

Gravitational, electromagnetic, strong and weak nuclear

Question 4

What is the equation for momentum?

Answer 4

Momentum = mass x velocity

Question 5

What is the unit for momentum?

Answer 5

kgms-1

Question 6

What is the principle of conservation of momentum?

Answer 6

For a system of interacting objects, the total momentum in a specific direction remains constant, as long as no external forces act on the system.
The momentum before and after a collision is the same.

Question 7

Talk about the momentum of a gun and a bullet

Answer 7

The bullet and the gun have the same momentum but the mass of the gun is much larger so the velocity is smaller.

Question 8

How is momentum calculated experimentally?

Answer 8

Measure the mass of the object using a weighing scale
Then measure its velocity with either a light gate, motion sensor or stopwatch and known distance
Then multiply the two together

Question 9

What is a perfectly elastic collision?

Answer 9

Kinetic energy is not transformed into other energies

It is a collision where momentum, energy and kinetic energy are conserved

Question 10

What is an inelastic collision?

Answer 10

Kinetic energy is transformed into other energies in the collision
Momentum and total energy is conserved but kinetic energy is not conserved

Question 11

What is newtons second law of motion?

Answer 11

The net force acting on an object is directly proportional to the rate of change of momentum and is in the same direction
Force is proportional to the rate of change of momentum

Question 12

What is the equation that links force and momentum?

Answer 12

Force = Change in momentum / Change in time

Question 13

In terms of momentum, how do airbags work?

Answer 13

The force is reduced by increasing the time to change the momentum

Question 14

Why is momentum conserved in collisions?

Answer 14

In a closed system the net forces on an object are zero.
Net forces are proportional to the rate of change of momentum so the change in momentum is zero.
So the momentum of objects must not change and momentum is always conserved

Question 15

What is impulse?

Answer 15

The change in momentum of an object is the impulse. Force multiplied by time

Question 16

How is impulse defined in an equation?

Answer 16

It is the force applied to an object multiplied by how long the force is applied

Question 17

What is the area of a force time graph equal to?

Answer 17

The impulse

and is also always the momentum of the object

Question 18

How can momentums in different directions be added?

Answer 18

Method a) They can be added using triganometry where the total momentum is equal to the momentum afterwards. Just draw a digram and join the momentums into a triangle
Method b) The momentums can be resolved into vertical and horizontal and then calculated. The momentums in x and y must be the same before and afterwards