PR Physics

Question 1

Newton’s third law

Answer 1

Objects exerting forces on each other will have forces w the same magnitude but opposite directions = action-reaction pair; remember this pair refers to forces put on DIFFERENT OBJECTS, so gravitational vs normal force CANNOT APPLY

Question 2

Pushing an object on earth and on the moon = different forces needed?

Answer 2

no – F = ma (specific for exerting force on an object, not gravitational pull) does not depend on weight, only mass

Question 3

Inverse square law for gravitation

Answer 3

gravitational force proportional to 1/r^2 (inversely proportional to radius squared

Question 4

When drawing out force diagrams for gravitation

Answer 4

always draw out the normal counterforce

Question 5

differences between kinetic friction and static friction

Answer 5

Kinetic friction: friction when there is motion
- Ff = µk*Fn (frictional force = coefficient of kinetic friction * normal force)

Static friction: friction when there is no motion

• uses maximum coefficient of static friction (bc its always greater than coefficient of kinetic friction) = this is the amount of force it takes to initiate movement. “force of static friction” is just the force exerted on an object (object doesn’t need to be moving)
• Ff, max = µs*Fn

Question 6

When net force is zero

Answer 6

opposite forces are equal

e.g. when an object isn’t being lifted, the total upward force is equal to the total downward force (so if there’s an Fy but object is not being lifted, Fg = Fn + Fy, or normal force is not equal to gravitational force

Question 7

since ya don’t wanna memorize the big 5 equations, what do you need to know to derive the answers?

Answer 7

a = (vf-v0)/t; Remember v0 is often zero.
AND
vf-v0/2 = d/t; because v is average v, which is calculated using vf-v0/2.

Question 8

sqrt(3)/2 – value and why relevant

Answer 8

0.85, value for sin 60 and cos 30

Question 9

applied force F on an object from rest to start going up an incline requires which forces to be overcome?

Answer 9

both static force and gravitational force

Question 10

Will the centripetal force of an object increase or decrease with an increase in radius

Answer 10

Although acceleration = velocity^2/radius, velocity in this case refers to terminal velocity

terminal velocity = r*ω, where ω is the constant rotational velocity.

therefore, acceleration is proportional to r^2/r, or acceleration is proportional to r