Physics Class 1

Question 1

Newton’s First Law

Answer 1

Law of inertia

• an object in motion tends to stay in motion
• an object at rest tends to stay at rest
• velocity only changes with an applied net force

Question 2

Newton’s Second Law

Answer 2

Fnet = m a

Force ∝ a

Question 3

What does it mean if Fnet = 0

Answer 3

Velocity is not 0 too, it just means velocity is constant

Question 4

Weight formula

Answer 4

W = m g

Question 5

Newton’s Third Law

Answer 5

For every action there’s an equal & opposite reaction

• do not cancel out
• equal in magnitude and opposite in direction

Question 6

Normal force

Answer 6

force a surface exerts to keep itself intact

- direction is normal (perpendicular) to surface

Question 7

Kinetic friction vs static friction

Answer 7

Kinetic friction
Fk = μk Fn
Use: skidding or slipping
- Direction opposes velocity

Static friction
Fs μs Fn
Use: no motion relative to contact surface or rolling without slipping
- Direction opposes other forces

Question 8

How to know to use μk or μs

Answer 8

1. Find Fsmax —> μs x Fn
2. Does Fapplied > Fsmax? If yes, use μk because there will be slippage, if not then Fs = Fapp

If yes…

3. Use kinetic friction formula to find the force of friction (Fk = μk x Fn)
   * Fn will be in the x direction

Question 9

Force of tension

Answer 9

Always directed along the rope, away from object it’s connected to
- tension is same throughout any single rope

Question 10

How to calculate acceleration of masses?

Answer 10

1. Set a positive direction of rotation for pulley
2. Determine net force acting on system of masses (tensions cancel out)
   3, aooky Fnet = mtotal x a

Question 11

An object undoing nonzero acceleration is…

Answer 11

• turning at constant speed
• slowing down
• speeding up

Question 12

Which is larger usually - μs or μk?

Answer 12

μs