Honors Physics 9 Final Study Guide — Complete Answers

Section 1: Basic Concepts

1) What is acceleration?
Acceleration is the rate at which velocity changes over time. Unit: m/s².

2) What is velocity?
Velocity is speed with a direction. Unit: m/s.

3) What is momentum?
Momentum is mass times velocity: p=m×vp = m \times vp=m×v. Unit: kg·m/s.

4) What is energy?
Energy is the ability to do work. Unit: Joules (J).

5) What is the law of conservation of energy?
Energy cannot be created or destroyed, only transformed.

6) What are Newton’s Three Laws of Motion?

• 1st: Objects keep their motion unless acted on by force.

• 2nd: F=m×aF = m \times aF=m×a.

• 3rd: Every action has equal and opposite reaction.

7) What is a vector? What is a scalar?
Vectors have magnitude and direction. Scalars have only magnitude.

8) Examples of vectors and scalars:
Vectors: velocity, force, momentum.
Scalars: speed, distance, mass.

9) What is the Pythagorean Theorem?
c2=a2+b2c^2 = a^2 + b^2c2=a2+b2 for right triangles.

10) Free fall equations:

• v=v0+gtv = v_0 + g tv=v0​+gt

• d=v0t+12gt2d = v_0 t + \frac{1}{2} g t^2d=v0​t+21​gt2

• v2=v02+2gdv^2 = v_0^2 + 2 g dv2=v02​+2gd
  (with g=9.8m/s2g = 9.8 m/s^2g=9.8m/s2)

11) Metric prefixes:
kilo (k) = 1,000
centi (c) = 0.01
milli (m) = 0.001
micro (μ) = 0.000001

Section 2: Newton’s 3rd Law of Motion

12) Interaction between two objects:
Two objects exert forces on each other at the same time.

13) Newton’s 3rd Law:
Every action force has an equal and opposite reaction force.

14) Force pair:
Two forces equal in size and opposite in direction acting on different objects.

15) Four conditions for force pairs:

• Act on two different objects

• Equal magnitude

• Opposite direction

• Happen simultaneously

16) System in science:
Group of interacting objects (e.g., cannon and cannonball).

17) Cannon vs cannonball acceleration:
Cannonball has smaller mass → larger acceleration; cannon has larger mass → smaller acceleration.

18) Adding vectors:
Add components or use tip-to-tail method.

19) Resultant vector:
Single vector that replaces multiple vectors.

20) Calculate resultant vector:
Use Pythagorean Theorem: R=Vx2+Vy2R = \sqrt{V_x^2 + V_y^2}R=Vx2​+Vy2​​.

21) Vector components:
Parts of a vector along x and y axes.

22) Calculate vector components:
Vx=Vcos⁡θV_x = V \cos \thetaVx​=Vcosθ, Vy=Vsin⁡θV_y = V \sin \thetaVy​=Vsinθ.

Section 3: Momentum

23) Momentum:
Mass times velocity, p=m×vp = m \times vp=m×v.

24) Momentum formula:
p=mvp = m vp=mv.

25) Impulse:
Change in momentum.

26) Impulse formula:
J=F×ΔtJ = F \times \Delta tJ=F×Δt.

27) Impulse-momentum theorem:
Impulse equals change in momentum, J=ΔpJ = \Delta pJ=Δp.

28) Common form:
FΔt=mΔvF \Delta t = m \Delta vFΔt=mΔv.

29) Boxer riding with punch:
Increases impact time, reduces force.

30) Bouncing effect on impulse:
Bouncing increases impulse because momentum change is larger.

31) Bouncing effect on momentum change:
Momentum change doubles when bouncing.

32) Law of conservation of momentum:
Total momentum before collision equals total momentum after.

33) Momentum in collisions:
Momentum is always conserved.

34) Elastic collision:
Objects bounce off without loss of kinetic energy.

35) Elastic collision formula:
Momentum and kinetic energy both conserved.

36) Inelastic collision:
Objects stick together, kinetic energy not conserved.

37) Inelastic collision formula:
Use conservation of momentum only.

38) Non-head-on collision:
Momentum still conserved in all directions.

Section 4: Energy

39) Work:
Force applied times displacement in direction of force.

40) Carrying 50 lb weight no work:
No displacement in direction of force (holding still).

41) Work formula:
W=F×d×cos⁡θW = F \times d \times \cos \thetaW=F×d×cosθ.

42) Power:
Rate of doing work.

43) Power formula:
P=WtP = \frac{W}{t}P=tW​.

44) Mechanical energy:
Sum of kinetic and potential energy.

45) Potential energy:
Stored energy due to position.

46) Kinetic energy:
Energy due to motion.

47) Energy formulas:

• PE=mghPE = m g hPE=mgh

• KE=12mv2KE = \frac{1}{2} m v^2KE=21​mv2

• ME=PE+KEME = PE + KEME=PE+KE

48) Rollercoaster energy:
Max KE at lowest point, max PE at highest point.

49) Energy conserved on rollercoaster:
Mechanical energy (if no friction).

50) Efficiency:
Ratio of useful output energy to input energy.

51) Efficiency formula:
Efficiency=useful energy outputtotal energy input×100%\text{Efficiency} = \frac{\text{useful energy output}}{\text{total energy input}} \times 100\%Efficiency=total energy inputuseful energy output​×100%.

Section 5: Rotational Motion

52) Tangential speed:
Speed along the edge of a rotating object.

53) Rotational speed:
Number of rotations per unit time.

54) Relation of tangential and rotational speed:
Tangential speed = radius × rotational speed.

55) Rotational inertia:
Resistance to change in rotation; depends on mass distribution.

56) Torque:
Rotational equivalent of force.

57) Torque formula:
τ=r×F×sin⁡θ\tau = r \times F \times \sin \thetaτ=r×F×sinθ.

58) Center of mass:
Average position of mass in an object.

59) Center of gravity:
Point where gravity appears to act.

60) Rotation point:
Objects rotate about their axis or pivot point.

61) Center of mass fixed?
Not always; it can move.

62) Center of mass inside object?
Not necessarily; can be outside.

63) Stability:
Determined by position of center of mass relative to base.

64) Centripetal force:
Force that keeps an object moving in a circle, directed inward.
Formula: Fc=mv2rF_c = \frac{m v^2}{r}Fc​=rmv2​.

65) Centrifugal force:
Apparent force pushing outward in a rotating frame (not a real force).

66) When centrifugal force exists:
Only in rotating (non-inertial) reference frames.

67) Linear vs angular momentum:
Linear momentum is straight-line motion; angular momentum is rotational.

68) Angular momentum formulas:

• L=IωL = I \omegaL=Iω (moment of inertia × angular velocity)

• L=mvrL = m v rL=mvr (mass × tangential velocity × radius)

69) Conservation of angular momentum:
Angular momentum stays constant if no external torque acts.