Forces and motion test revision

Question 1

equation of force of moving objects

Answer 1

F=ma
Force = mass x acceleration

Question 2

If an object falls faster, how does air resistance change, and how does it hit air particles

Answer 2

Hits more air particles and hits them harder so increases air resistance

Question 3

Air resistance increases by how much when the speed doubles

Answer 3

A factor of four

Question 4

How can air resistance be reduced

Answer 4

By streamlining (reducing area at right angles to the motion)

Question 5

Describe the relationship between speed and forces on falling objects

Answer 5

When an object is falling slowly, the forces are unbalanced so it speeds up, so the air resistance also increases, until the forces re balanced. This means acceleration stops and velocity remains constant. This is called terminal velocity.

Question 6

Forces on a skydiver

Answer 6

1. As soon as they jump out, the only force is weight, so they accelerate towards the ground
2. Then comes air resistance thanks to particles, but weight is still larger so continue to accelerate
3. As velocity increases, as does air resistance so at a point, the forces will be balanced. no resultant force, so constant velocity (terminal velocity)
4. At this point, sky diver opens parachute. Larger surface area means much larger air resistance. Greater air resistance than weight so deceleration.
   Velocity decreases, so does air resistance so once again forces will eventually be balanced, so lower terminal velocity