Dynamics

Question 1

Mass

Answer 1

the amount of matter in an object

• the property that resists a change in motion

Question 2

Weight

Answer 2

the effect of a gravitational field on a mass

Question 3

Equation of weight

Answer 3

W = mg

Question 4

Explain free fall of an object

Answer 4

An object in free fall is falling solely under the influence of gravity

On Earth, all free-falling objects accelerate towards Earth at a rate of 9.81 m s−2

In the absence of air resistance, all bodies near the Earth fall with the same acceleration regardless of their mass

Question 5

Equation of force

Answer 5

F = ma

Newton’s Second Law of Motion tells us that objects will accelerate if there is a resultant force acting upon them

This acceleration will be in the same direction as this resultant force

Question 6

Resultant force

Answer 6

the vector sum of all the forces acting on the body.

Question 7

Is acceleration a vector?

Answer 7

Since acceleration is also a vector, it can be either positive or negative depending on the direction of the resultant force

Negative acceleration is deceleration

An object may continue in the same direction however with a resultant force in the opposite direction to its motion, it will slow down and eventually come to a stop

Question 8

Newtons 1st law

Answer 8

A body will remain at rest or move with constant velocity unless acted on by a resultant force

Question 9

Newtons 2nd law

Answer 9

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force

Question 10

Newtons 3rd law

Answer 10

If body A exerts a force on body B, then body B will exert a force on body A of equal magnitude but in the opposite direction

Question 11

Requirements for Newtons 3rd law to work

Answer 11

must act on different objects
must also be of the same type e.g. gravitational or frictional

Question 12

Principle of conservation of momentum

Answer 12

The total momentum of a system remains constant provided no external force acts on it

total momentum before a collision = total momentum after a collision

Remember momentum is a vector quantity. This allows oppositely-directed vectors to cancel out so the momentum of the system as a whole is zero

Momentum is always conserved over time

Question 13

External forces

Answer 13

forces that act on a structure from outside e.g. friction and weight

Question 14

Internal forces

Answer 14

forces exchanged by the particles in the system e.g. tension in a string

Question 15

What do you call a system with no external forces

Answer 15

a closed system

Question 16

Equation of momentum

Answer 16

p = m x v

momentum = mass x velocity

Question 17

momentum before = momentum after equation

Answer 17

M1V1 + M2V2 = M1V1’ + M2V2’

Question 18

Elastic collision

Answer 18

when two objects collide with each other, momentum and kinetic energy are both conserved

Question 19

Inelastic collision

Answer 19

when two objects collide with each other, momentum is conserved but kinetic energy is not conserved

Question 20

Explain perfectly elastic collision

Answer 20

When two objects collide, they may spring apart retaining all of their kinetic energy.

Since kinetic energy depends on the speed of an object, in a perfectly elastic collision (head-on approach) the relative speed of approach = the relative speed of separation

Question 21

Equation for kinetic energy

Answer 21

1/2mv^2

Question 22

Explain perfectly inelastic collision

Answer 22

when two objects collide, they stick to each other after the collision and move in the same direction

Question 23

Elastic collision formula

Answer 23

m1v1 + m2v2 = m1v1’ + m2v2’

Question 24

Inelastic collision formula

Answer 24

V = (m1v1 + m2v2) / (m1 + m2)