[SEC 3] CHAPTER 4 - dynamics

Question 1

what is Newtons first law of motion?

Answer 1

when there is no net force acting on a body, the body will continue with whatever motion it has

Question 2

Does FR = 0N mean that there is no force?

Answer 2

No. It just means that forces are balanced

Question 3

What is newtons second law?

Answer 3

when a net or resultant force acts on an object of constant mass, the object will accelerate and move in the direction of the resultant force

Question 4

FR = ?

Answer 4

FR = ma

resultant force = mass x acceleration

Question 5

friction is a contact force that opposes a pulling/pushing force what is the equation?

Answer 5

net force = pull - friction

OR

net force = push - friction

Question 6

describe the motion on a typical sky diver diving in a velocity time graph from T = 0 - 3s

Answer 6

At T = 0 - 3s, only weight is acting on sky diver. Air resistance is negligible. Sky diver experiences free fall acceleration of 10ms^-2

Question 7

describe the motion on a typical sky diver diving in a velocity time graph from T = 3 - 10s

Answer 7

At T = 3 - 10s, air resistance increases as speed of skydiver increases. However, air resistance is smaller than weight. Resultant force downwards decreases. Sky diver experiences decreasing acceleration

Question 8

describe the motion on a typical sky diver diving in a velocity time graph from T = 10 - 20s

Answer 8

At T = 10 - 20s, resultant force is zero since air resistance is equal to weight. Sky diver moves at terminal velocity.

Question 9

describe the motion on a typical sky diver diving in a velocity time graph from T = 20 - 22s

Answer 9

At T = 20 - 22s, Resultant force is upwards and negative since air resistance is greater than weight. Negative acceleration shows that the skydiver decelerates

Question 10

describe the motion on a typical sky diver diving in a velocity time graph from T = 22 - 35s

Answer 10

At T = 22 - 35s, air resistance decreases as speed of skydiver decreases. Eventually, Air resistance is equal to weight. Resultant force is zero and there is no acceleration. Skydiver moves at a slower terminal velocity than during T = 3 - 10s

Question 11

what is newtons third law?

Answer 11

for every action there is always an equal and opposite reaction

Question 12

what are the characteristics of action and reaction pair of forces?

Answer 12

action and reaction pair of forces:
1. are in opposite direction
2. are equal in magnitute
3. are on different bodies
4. are of the same type

Question 13

why do objects keep accelerating in a vacuum?

Answer 13

there is no terminal velocity, as there is no air resistance to cancel out the weight of the object

Question 14

why do objects reach terminal velocity in air?

Answer 14

air resistance will increase for the forces to be balanced