3 - Forces and Motion

Question 1

What is the difference between a vector and scalar quantity?

Answer 1

A vector quantity is a quantity with both magnitude and direction (e.g. velocity, displacement, force). A scalar only has a magnitude (e..g. speed, distance).

Question 2

How is displacement different to distance?

Answer 2

Displacement is the distance travelled in relation to the starting point in one straight line whereas distance is the total distance travelled, where direction is not considered.

Question 3

Flat line on dt graph

Answer 3

object stationary

Question 4

Straight sloping lines on dt graph

Answer 4

object travelling at constant speed (steeper = faster)

Question 5

gradient of dt graph

Answer 5

velocity

Question 6

flat line on vt graph

Answer 6

constant velocity

Question 7

straight sloping lines on vt graph

Answer 7

constant acceleration (steeper = the faster the object is speeding up or slowing down)

Question 8

gradient of vt graph

Answer 8

acceleration

Question 9

area under vt graph

Answer 9

distance travelled (displacement)

Question 10

Stopping distance

Answer 10

the distance a vehicle will travel between the moment a danger is spotted to when the vehicle has completely stopped (sum of thinking and braking distance)

Question 11

Thinking distance

Answer 11

distance travelled between when the driver sees the danger to when they first apply the brakes

Question 12

Braking distance

Answer 12

distance travelled between when the driver applies the brakes to when the vehicle has fully stopped

Question 13

Factors affecting thinking distance

Answer 13

speed, drugs, alcohol, tiredness, distractions

Question 13

Factors affecting thinking distance

Answer 13

speed, drugs, alcohol, tiredness, distractions

Question 14

Factors affecting braking distance

Answer 14

speed, mass, condition of brakes, tyre conditions (e.g. pressure), road conditions (e.g. slope, ice, gravel, weather), aerodynamics of car

Question 15

Thinking distance proportionality

Answer 15

Thinking distance ∝ speed (d=st so d∝s, W=Fd so E (energy transferred) = Fst so E∝s)

Question 16

Braking distance proportionality

Answer 16

Braking distance ∝ speed^2 (E=0.5mv^2 so E∝v^2)

Question 17

Journey of skydiver

Answer 17

At the start of his jump the air resistance is small so he accelerates downwards.As his speed increases his air resistance will increase. Eventually the air resistance will be big enough to balance the skydiver’s weight. At this point the forces are balanced so his speed becomes constant this is called TERMINAL VELOCITY. When he opens his parachute the air resistance suddenly increases, causing him to start slowing down. Because he is slowing down his air resistance will decrease again until it balances his weight. The skydiver has now reached a new, lower terminal velocity

Question 18

As speed increases, air resistance…

Answer 18

increases

Question 19

Horizontal motion in projectile qs

Answer 19

Air resistance is assumed to have no effect on horizontal motion so horizontal acceleration is 0