PhysicsFinal Exam

Review-2015

Horizontal and Vertical Motion

Define• Displacement

– The straight line distance drawn from the object’s initial position to the object’s final position• ΔX= Xf-Xi

• Velocity – The displacement divided by the time interval during

which the displacement occurred.• V = ΔX/Δt

• Acceleration– The rate of an object’s change in velocity.

• a = ΔV/Δt

If an object moves with a constant

velocity, what is it’s acceleration?

ZERO!!!!It does not speed up or slow down!

Which Runner is Faster????

Runner 1 is faster – the slope of the position vs. time graph is steeper!

Runner 2 is slower – the slope of the position vs. time graph is less steep.

The ball is shown at each 1 second interval. Assuming only gravity acts on the ball, write in the velocity of the ball at each second.

39.2m/s

29.4m/s

19.6m/s

9.8m/s

0m/s 0m/s

-9.8m/s

-19.6m/s

-29.4m/s

-39.2m/s

-49m/s 49m/s

Atmosphere or Vacuum?

Did these objects fall in an atmosphere or a vacuum?How do you know?

Galileo's theory states that all objects will accelerate due to gravity at the same rate, regardless of mass, shape or size.

1. How far does a car travel if, starting with a velocity of 2m/s, it drives for 5 seconds while accelerating at 4m/s2?

Δx =Vi =

Δt =a =

?2m/s5s

4m/s2

Δx = ViΔt + ½aΔt2

Δx = (2m/s)(5s) + ½(4m/s2)(5s)2

Δx = (2m/s)(5s) + ½(4m/s2)(25s2)

Δx = (10m) + ½(100m)Δx = 10m + 50m

Δx = 60m2. Cristal bikes with a velocity of 12m/s and then accelerates at 3

m/s2 for 20m. What is her final velocity?

Vi = 12m/sVf = ?Δx= 20ma = 3m/s2

Vf 2= Vi2 + 2a∆x

Vf 2 = (12m/s)2 + 2(3m/s2)(20m)

Vf 2 = (144m2/s2) + 2(3m/s2)(20m)

Vf 2 = 144m2/s2 + 120m2/s2

Vf 2 = 264m2/s2

Vf = 16.2m/s

3. Edelin started to drive her car with an initial velocity of 20m/s. If she drives for 6 seconds with an acceleration of 2m/s2, what is her final velocity?

Vi =

Δt =a =Vf =

Vf = Vi + aΔt20m/s

6s

2m/s2

?

Vf = Vi + a Δt20m/s (2m/s2) (6s)

Vf = 20m/s+ (2m/s2)(6s)12m/sVf = 10m/s + 12m/s32m/s

Vf = 32m/s

4. How fast is a penny going right before it hits the ground if it is dropped from a building 150m high?

Δy = -150m

Vi = 0m/s

a = -9.8m/s2

Vf = ?

Vf2 = Vi

2+ 2(a)(Δy)

Vf2 = (0m/s)2 + 2(-9.8m/s2)(-150m)

Vf2 = 0 + (2940m2/s2)

Vf2 = 2940m2/s2

Vf = -54.2m/sVf

= +54.2m/s

“Forces and the Laws of Motion”

1. Define Force:2. Define Net Force:3. List 3 ways a Net Force can change

motion:4. Define Equilibrium:5. Which force diagram shows an object in

equilibrium?

6. An object in Equilibrium can have 2 motions:7. What is the net force on a box moving

with a constant velocity of 60m/s? 8. Draw a force diagram a) for a book at rest on

a table. b) for a book falling and accelerating downward.

1. Define Force:

2. Define Net Force:

3. List 3 ways a Net Force can change motion:

Push or a Pull

The sum of all the forces on an object.

Speed Up Slow Down

Change Direction

4. Define Equilibrium:

5. Which force diagram shows an object in equilibrium?

6. An object in Equilibrium can have 2 types of motion:

The forces on the object add to zero. FNet=0The forces on the object are balanced.

• Motionless (not moving)• Moving with a Constant

Velocity

(not speeding up, not slowing down, not changing direction)

7. What is the net force on a box moving with a constant velocity of 60m/s? constant velocity FNet = 0

8. FN (Normal Force)

(or F Table)

F air resistance

Fw (gravity)Fw (gravity)Different sized arrows show NET FORCE – accelerating!

Same sized arrows show EQUILIBRIUM– at rest or constant velocity!

1. What is Newton’s 1st Law of Motion? Give examples.

2. What is Newton’s 2nd Law of Motion? . Give examples

3. What is Newton’s 3rd Law of Motion?Give examples.

4. What happens when a cart with a big mass and a cart with a small mass are pushed with the same force?

5. What happens if a person is moving in a car and then the car suddenly stops?

6. What happens when a balloon filled with air is released?

1. What is Newton’s 1st Law of Motion?

“Inertia” “An object at rest will stay at rest andAn object in constant velocity motion will stay in constant velocity motion

Unless acted on by an unbalanced force.”Examples:Tablecloth trick, Hoop/Nuts,, Car Accidents (Seatbelts), Ball in Truck

2. What is Newton’s 2nd Law of Motion ?List at least two examples of the 2nd Law shown in class. “F=ma” “The acceleration of an object is directly proportional to

the force applied to object and inversely proportional to the object’s mass”

Examples:•Skateboarders, Basketball and Tennis Ball, Heavy and Light Carts, Earth and Object

3. What is Newton’s 3rd Law of Motion?List at least two examples of the 3rd Law shown in class. Action/Reaction “For every force applied to an object, the object

applies an equal and opposite force back.”

Examples: Balloon Rocket, Walking, “Pushing off table”, Newton’s Cradle, Punching A Face

4. What happens when a cart with a big mass and a cart with a small mass are pushed with the same force?

The cart with more mass took more time to reach the end of the track,

the cart with less mass got there faster!

So …

The more mass, the less acceleration!

Newton’s 2nd Law!

5. What happens if a person is moving in a car and then the car suddenly stops?

Newton’s 1st Law!!! If the car suddenly stops the person will continue moving. There was a force on the car, so the car stops. But there is no force on the person, so they continued moving. 6. What happens when a balloon filled with air is released?Newton’s 3rd Law!!

When released, The balloon moved forward and the air moved backwards.

The balloon pushed the air out (action),

so the air pushed the balloon too (reaction)!

1. What is the net force on a box which has a mass of 20kg and an acceleration of 5m/s2.

F = maF = (20kg) x ( 5m/s2)F = 100 kgm/s2

F = 100 N

F = ?m = 20kga = 5m/s2

2. What is the acceleration of a 200kg carpushed with a force of 600N?

a = ?m = 200kgF = 600N

F = ma600 N = (200kg) x (a)600 kgm/s2 = (200 kg)(a) 200kg 200kg 3m/s2 = a

“Circular Motion”

1. What is the centripetal force?

2. What provides the centripetal force in each case below:

A skateboard turning a corner.A person swinging on a swing set.The moon orbiting around the EarthA cart on a rollercoaster.3. Below is a diagram of a record spinning – which of the points is

moving with a greater tangential speed, the inside of outside?

Answer the following questions:

The force that pulls an object inward, and changes the direction of an object. It causes circular motion.

Friction between the ground and tire.

The rope

Gravity

The track

The outside point has a greater tangential speed.It has to cover more distance (circumference) in the same amount of time because it is farther from the center (has a greater radius).

1. A girl swings a bucket of water over her head so that it has a tangential speed of 6m/s. If the rope pulling the bucket is 0.75m long (radius), what is the bucket’s centripetal acceleration?

ac =Vt =r =

?6m/s0.75m

ac = Vt2

rac = __(6m/s)2

0.75m

ac = (36m2/s2) 0.75m

ac = 48m/s2

2. What is the centripetal force of a 500kg rollercoaster car being pushed around a track with a radius of 100m if its tangential speed is 25m/s?Fc = mVt

2

rFc = (500kg)(25m/s)2

100m

Fc = (500kg)(625m2/s2) 100m

Fc = (312500kgm2/s2) 100m

Fc = 3125N

m = 500kgVt = 25m/s

Fc = ?

r = 100m

“Energy and

Energy Conservation”

1. List the 5 types of Energy.

2. Write which type of Energy you listed above is present in each of the following examples:a)A bicycle coasting along a level roadb)Heating waterc)Microwave Oven used to heat foodd)Glowing embers in a campfire (hot coals).e)A strong windf)The Sun fusing hydrogen atoms into helium atomg)A swinging pendulumh)A rocket being launched into space.

Chemical, Electromagnetic, Nuclear, Mechanical, Thermal

MechanicalThermal

ElectromagneticThermal

MechanicalNuclear

MechanicalChemical

Kinetic Energy

EquationKE = ½mv2

The Energy of Motion

KE = ½(mass)x(velocity)2

Potential EnergyThe Energy of Position

Equation

PEg = mghPEg=(mass)x(gravity)x(height)

Point 1 Point 2 Point 3 Point 4 Point 5

PEg 900 J 550 J

KE 300 J

ME

Label the types of energy (PE or KE) the rollercoaster has at each point. Then Fill out the table below using the Law of the Conservation of Mechanical Energy

Note: •At point 1 the velocity is 0m/s. •Point 2 and 4 are at the lowest point.

0 J900 J 900 J 900 J 900 J 900 J

0 J 0 J

900J 350J 900J

600J

PE

KE

PE + KE

PE + KE

KE

1. Calculate the potential energy of the 10kg rock at the top of a 20m high cliff.

PE = ?m = 10kgh = 20m

PE = mghPE = (10kg)(9.8m/s2)(20m)

PE = 1960 J

2. Calculate the kinetic energy of the 10kg person moving at 5m/s at the bottom of a hill.

KE = ?m = 10kgv = 5m/s

KE = ½mv2

KE = ½ (10kg)(5m/s)2

KE = 125 J

“Impulse & Momentum”“The Conservation of Momentum”

• What is momentum?

• What is the equation for momentum?

• What does the Impulse-Momentum Theorem state?

• What does the “Law of the Conservation of Momentum” state?The total momentum of a system will stay the same before and after a collision.

p = mv

The product of an object’s mass and velocity

For a given change in momentum the more time applied to stop an object the less force needed to stop it.

Which object has more momentum?

p = mvp = (0.009kg)(500m/s)

p = 4.5kgm/s

p = mvp = (2kg)(2.25m/s)

p = 4.5kgm/s

They have the same momentum!

What type of protection do each of these offer?• Elastic bands in an egg-drop project.

• Bumpers that collapse of the front of a car.

• Helmets – for sports, biking, motorcycles etc…

• Highway guardrails.

• Spiderman’s web.

• Cell phone covers.

Suspension

Crumple Zone

Cushion

Crumple Zone

Suspension

Cushion

1. A person kicks a ball with a force of 108N if the person and the ball are in contact for 0.030s, what is the impulse (change in momentum)?

Δp = ?F = 108NΔt = 0.030s

Δp = FΔt

Δp = 108N(0.030s)

Δp = 3.25kgm/s

2. A man’s 1.5kg hand hits a punching bag with a velocity of 3m/s and it stops the man’s hand, what is the impulse (change in momentum)?

m = 1.5kgVi = 3m/sVf = 0m/sΔp = ?

Δp = mvf - mvi

Δp= (1.5kg)(0m/s) – (1.5kg)(3m/s)Δp= 0kgm/s – 4.5kgm/sΔp= – 4.5kgm/s

Perfectly Inelastic

For each of the following examples, identify the type of collision…

Elastic Perfectly Inelastic

Inelastic Perfectly Inelastic Elastic

Using the diagrams below, determine the missing variable for each collision.

70kgm/s

-450kgm/s

20kgm/s

Waves & Wave Properties

Sound Waves & Light Waves

Label the following examples as transverse or longitudinal waves.

transverse

longitudinal

Sound and Light Waves• Sound travels at approximately 340m/s in air.• Light travels at 300,000,000m/s (3x108m/s) in a vacuum.

• Why do you see lightening before you hear it?– Because light travels faster than sound.

• Why is it wrong to see and hear an explosion in outer-space? - Light can travel in a vacuum --- sound cannot travel in a

vacuum.- So in outer space you can SEE things – but you can’t hear them!

Moving towards– higher frequency

High frequency means high pitch!

When does the person hear a higher pitch? When the car moves towards or away from him?

When does the person see a redder wave? (red shift) When the light source is moving toward or away from him?

lower frequency (redder waves)(moving away)

Electromagnetic Spectrum “Light Waves”• Parts of the Electromagnetic Spectrum have different properties.• These properties are based on their frequency and wavelength.

fλ

Low Energy

fλ

High Energy

1. What wave has the highest frequency?

2. Which wave has a higher wavelength than microwaves?

3. Which wave moves the fastest through a vacuum?

Gamma rays

Radio waves

They all have the same speed – the SPEED OF LIGHT!

1. A water wave has a frequency of about 300Hz and a wavelength of 2.5m, what is the speed of this wave?

V=f λV = 300Hz(2.5m)

V = 750m/s

V = ?f = 300 Hzλ = 2.5m

2. A guitar emits frequencies that range from a low of about 50Hz . Find the wavelength in air when the speed of sound is air is 340m/s.

V = 340m/sf = 50 Hzλ = ?

V=f λ340m/s = 50Hz(λ)

6.8m = (λ)50 Hz50 Hz