Chapter 3. Dynamics

Question 1

Note

Answer 1

Newton’s laws break down at speeds close to the speed of light

Question 2

What is inertia?

Answer 2

The reluctance of an object to change it’s state(in motion or stationary)

Question 3

What is mass?

Answer 3

A measure of a body’s inertia

Question 4

What is Newton’s first law?

Answer 4

A body at rest will stay at rest and a body in motion will continue in motion in a specified direction unless a resultant force acts on it.

Question 5

What is momentum?

Answer 5

A product of mass and velocity.
momentum,p(kgms^-1) = mass,m(kg) x velocity,v(ms^-1)
it is a vector quantity

Question 6

What is Newton’s second law?

Answer 6

The rate of change of momentum of an object is directly proportional to the resultant force acting on it. The change in momentum takes place in the direction of that force

Question 7

Define a newton

Answer 7

One newton is the resultant force needed to cause a rate of change of momentum of 1kgms^-2
One newton is the resultant force needed to give a mass of 1kg an acceleration of 1ms^-2

Question 8

What is Newton’s third law?

Answer 8

To every action there’s an equal but opposite reaction.

Question 9

Identifying Newton’s third law pairs

Answer 9

-Force pairs act on different objects
-Force pairs have the same magnitude
-Force pairs act along the same line but in opposite directions
-Force pairs act for the same time
-Force pairs are of the same type

Question 10

What is impulse?

Answer 10

The effect of a force
force x time
1Ns = 1kgms^-1

Question 11

What does the area under a force-time graph represent?

Answer 11

impulse=change in momentum

Question 12

What is the principle of conservation of momentum?

Answer 12

Whenever objects interact, their total momentum in any direction remains constant, provided that no external force acts on the objects in that direction.
Total linear momentum before the interaction = Total linear momentum after interaction

Question 13

Note

Answer 13

Make sure the momentum is in the same direction before applying the law of conservation of momentum

Question 14

What is dynamics”

Answer 14

Dynamics is the study of forces and their effect on motion as opposed to kinematics which is thestudy of motion regardless of the cause of the motion or the mass of the object.

Question 15

Note

Answer 15

In an elastic collision kinetic energy is conserved
Relative velocity of approach(u1 - u2) should be equal to negative the relative velocity of separation(v1 - v2)

Question 16

Note

Answer 16

In an inelastic collision some of the initial kinetic energy is changed to other forms, kinetic energy is less after the collision
-momentum is conserved

Question 17

Note

Answer 17

In a totally inelastic collision the relative velocity of separation = 0
A large ammount of kinetic energy is lost