Review for Test (Newton’s 2nd and 3rd Laws)



Name: ______________________________ Date: ______________ Hr: _____

Review for Test (Newton’s 2nd and 3rd Laws)

Complete the review and hand it in the day of the test. Your bellringers are due on this day as well.

Vocabulary: Define each of the following terms

• Acceleration

Change in speed and/or direction in a certain period of time (ex units: m/s2 or m/s/s)

• Free fall

When an object is falling and is only affected by gravity

• Newton

the amount of force needed to move a 1 kg mass object at an acceleration of 1 m/s2

• Equilibrium

Net force of 0 N, object is at rest OR moving with constant speed and direction

• Inversely Proportional

If you increase one, the other decreases. EXAMPLE: F=ma shows if m increases by 2, then a will decrease by 2 (divide by 2)

• Directly Proportional

If you increase one, the other increases at same rate. EXAMPLE: F=ma shows if F increases by 3, then a will increase by 3

• Vector Quantities (list the 4 examples along with your definition)

Quantities that include magnitude (size, #) and direction

Acceleration, Velocity, Force, Displacement

Newton’s 2nd Law

1. Calculate the acceleration of a jet car racing on the Bonneville Salt Flats if the force on the car is 500,000 N and the mass is 2,100 grams

a = F/m

= 500,000 N

2.1 kg

= 238,095.24 m/s2 forward

2. Your bicycle has a mass of 9.1 kg. You accelerate at a rate of 1.79 m/s2. Calculate the net force accelerating the bicycle.

F = ma

= (9.1 kg)(1.79 m/s2)

= 16.29 N forward

3. On that bicycle (from #2), you travel for 5 min down a gradual hill. If your initial velocity was 2 m/s, what was the final velocity?

5 min x 60 s = 300 s

1 min

Vf = at + Vi

= (1.79 m/s2)(300 s) + 2 m/s

= 539 m/s downhill

4. A whale is lifted into the air by a crane. The crane must exert an unbalanced force of 800 N to lift the whale from rest. If the acceleration of the object was 10 m/s2, what is the mass of the object in kg?

m = F/a

= (800 N) / 10m/s2

= 80 kg

5. The speed of sound at sea level is 761.2 mph. If a sound was traveling for 45 seconds, how many miles did it travel?

45 sec x 1 min x 1 hr = 0.0125 hr

60 s 60 min

d = s * t

= (761.2 mi/hr)(0.0125 hr)

= 9.515 mi

6. What is the change in velocity experienced by a ball rolling 40 m down a hill for 3 min at an acceleration of 2.3 m/min2?

∆ V = A * T

= (2.3 m/min2)(3 min)

= 6.9 m/min

7. If a car has no acceleration, can it be moving? Explain.

Yes- if it began with a positive velocity, it will continue with the same velocity (not changing direction OR speed)

8. When an object is in free fall, what force(s) are acting on it? What the value of its rate of acceleration?

9.8 m/s2 - rate of acceleration due to gravity (g)

9. Using relationships described in Newton’s 2nd law, answer the following questions

a. An object accelerates at 2 m/hr/s. If the net force increases by 4, what is the new acceleration? (assume mass constant)

F = ma

4 = 1 * a (4 b/c force increases by that amount, 1 b/c mass isn’t changing)

4 = a

4 * original = 8 mi/hr/s

b. An object has a mass of 3 kg. If the acceleration doubles, what will the new mass be? (assume force constant)

F = ma

1 = m * 2 (2 b/c accel increases by that amount, 1 b/c force isn’t changing)

1 = 2m

½ = m

½ * original = 1.5 kg

c. An object is experiencing a force of 10 N. If the mass doubles, what should happen to the force? (assume acceleration constant)

F = ma

F = 2 * 1 (2 b/c mass increases by that amount, 1 b/c accel isn’t changing)

F = 2

2 * original = 20 N

d. An object has an acceleration of 5 m/s/s. If the mass decreases by 3, what is the new acceleration? (assume force constant)

F = ma

1 = 1/3 * a (1/3 b/c mass decreases by 3, 1 b/c force isn’t changing)

3 = a

3 * original = 15 m/s/s

***Note: for numbers 10 – 12, you don’t have to use the same values for force. The idea is that the horizontal net force is equal to what is described in the question.

10. Draw a force diagram showing the four main forces on an object that is accelerating to the left with a net force of 10 N left.

11. Draw a force diagram showing an object traveling at a constant speed.

12. Draw a force diagram of an object that is traveling to the right and decelerating with a net force of 5 N.

13. Describe the three types of friction and give examples of when each would be present.

Sliding: feet on the floor when walking down the hall (two solids)

Rolling: Car wheels (round object on a solid)

Fluid: Bird flying (moving through a gas or liquid)

Newton’s 3rd Law

1. Identify the action and reaction forces in the examples below:

a. A hammer hits a nail.

Action: Hammer on nail, Reaction: nail hits hammer

b. Earth’s gravity pulls down on the moon

Action: Earth gravity pulls on moon, Reaction: moon gravity pulls on earth

c. A helicopter blade pushes air downward.

Action: blade pushes down on air, Reaction: air pushes up on blade

d. You step off a curb

Action: feet push onto curb, Reaction: curb pushes onto feet

e. You pat your friend on the back

Action: hand pushes on back, Reaction: back pushes on hand

f. A wave hits a rocky shore.

Action: wave hits shore, Reaction: shore pushes against wave

2. If a car hits a wall with a force of 400 N, what is the reaction force and how large is it?

Action = 400 N, car pushes on wall; Reaction = 400 N, wall pushes on car

Graphing

1. What does the slope of a position (distance) versus time graph represent?

Speed or velocity (slope = rise/run = d/t)

2. What does the slope of a speed (velocity) versus time graph represent?

Acceleration (slope = rise/run = v/t)

3. On the graphs below, identify the direction of travel and describe the motion (accelerating, decelerating, resting, constant velocity) of each object.

[pic]

[pic]

Units

Do the units below represent acceleration (a), force (F), velocity (V), time (t), or distance (d)?

|cm d |hr t |

|m/min2 a |mi/hr/s a |

|m/min/min a |km/s V |

|m/min V |cm/s2 a |

|N F |mi/hr V |

ESSAY QUESTION

For the essay question, you will be presented with three scenarios. Each scenario will apply to ONE of Newton’s 3 Laws. You will have to identify which law applies, tell me what the law says, and explain why that situation applies to that law. Practice using the scenarios below.

• When a rocket is launched, hot gas is pushed out of the bottom as the rocket is thrust upward.

• Third Law

• Every action has equal and opposite reaction

• Action force is gas pushing downward onto ground, reaction is ground pushing upward on gas making the rocket launch

• In order to have enough force, a karate sensei (master) must use his entire body's mass in breaking bricks.

• Second Law

• Mass is inversely proportional to acceleration, F = ma

• More mass = more force so bricks break as long as acceleration remains constant

• I was in a car accident where I hit the windshield with my head. I was not wearing my seatbelt.

• First Law

• Object in motion stays in motion with same speed direction, unless acted on by outside force

• My body continued to move in the direction/speed the car was previously moving. The windshield was an outside force which stopped my movement. The seatbelt would’ve stopped me if I had been wearing it.

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5 N

15 N

5 N

5 N

5 N

10 N

10 N

5 N

5 N

13 N

8 N

5 N

constant speed, E

constant speed, W

constant speed E (slower than A)

at rest (east of starting point)

acceleration, E

W

Object A

Object B

Object C

Object D

Object E

E

A

B

C

D

E

constant speed, S

accel, N

Decel, N

Accel S

Decel S

Constant Speed N

North

South

A

C

D

E

F

B

Object A

Object B

Object C

Object D

Object E

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Object F

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