Unit 1-3 Review 1. Calculate acceleration, distance, velocity & time Read position-time, velocity time graphs Define velocity, speed and acceleration.

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Physics SemesterUnit 1-3 Review

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Unit 1 – Motion Calculate acceleration, distance, velocity & timeRead position-time, velocity time graphsDefine velocity, speed and acceleration

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If Joe speeds up from 30 m/s to 45 m/s in 3 seconds, what is his acceleration?

A = 15 m/s ÷ 3 sec = 5 m/s/s

Calculate - Acceleration

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If Jill drives at 30 m in 6 seconds. What is her velocity?

V = D ÷ t 30 m ÷ 6 sec 5 m/s

Calculate - velocity

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If Chase drives 30 m/s for 7 seconds, how far has he gone?

D = V × T 30 m/s × 7 sec = 210 m

Calculate - distance

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If Seth travels 300 m at 15 m/s, how long did it take him to get there?

T = D ÷ V 300 m ÷ 15 m/s = 20 sec

Calculate - time

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What is the velocity of the following object? It appears that the object went 80 cm in 0.4

sec. V = Δx / t = 80 cm / 0.4 sec = 200 cm/s

Calculate velocity from a graph

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In this position time graph, which object has a positive velocity?

Negative? Not moving? Going the fastest? Remember that the

steeper the graph, the faster the speed and that negative graphs have a negative velocity.

Read x-t Graph

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Which graph shows a positive acceleration?

Negative? Zero?

Remember that the slope of an x-t gives the velocity and the slope of the v-t gives the acceleration.

Read v-t Graph

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Distance ÷ time Zero if not moving Positive in a positive direction Negative in a negative direction The slope of an x-t (position-time) graph

Instantaneous at a given instant Average looking at totals (change in) = acceleration × time

Define Speed

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Change in velocity ÷ timeSlope of a velocity-time (v-t) graph

Speeding upSlowing downChanging direction If an object does not accelerate, it moves at a constant velocity

Define acceleration

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Starting position?◦ High positive

Starting velocity?◦ Zero

Final velocity?◦ High negative

Acceleration?◦ Negative

Motion?◦ Speeding up (both v-t and a-t

on the bottom)

Stack of Graphs

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Unit 2 - ForceF = maNet forceNewton’s LawsMomentum

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Force = mass × acceleration

If a 7 kg ball is accelerated at 3 m/s/s how much force is needed?

F = 7kg × 3 m/s/s = 21 N

F = ma

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If a rock is hanging from a rope and there is 70 N of tension force up from the rope and 70 N of gravitational force down from the Earth, what is the net force?

ZERO!!! Equilibrium – all forces cancel

each other out, they are balanced.

Net force

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If a rock is sliding down a ramp with 12 N of force and there is 5 N of friction on the ramp, what is the net force?

7N down 12 – 5 = 7

Net Force 2

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Net force is Zero for objects at rest or moving at a constant velocity (cruise control).

Positive for objects with a positive acceleration (speeding up)

Negative for objects with a negative acceleration (slowing down)

Net force - definitions

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An object in motion or at rest will stay in motion or at rest unless acted on by an unbalance (net) force.

Law of InertiaObjects want to keep doing what they are doing.

Newton’s 1st Law

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An object will accelerate in the direction force is applied, and force equals mass times acceleration.

F = ma It takes more force to accelerate a heavier mass at the same rate.◦A 5 year old can’t throw as hard or fast as a

15 year old.

Newton’s 2nd Law

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For every action force, there is an equal and opposite reaction force.

Action-reaction forces are equal in size and opposite in direction.

Newton’s 3rd Law

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P = mvWhat is the momentum of a 5 kg rock moving at 2 m/s?

P = 5 kg × 2 m/s = 10 kgm/s

Momentum

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Unit 3 - Energy

W = FDP = W/tEk = ½ mv2

Eg = mgy6 forms of energy

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Work = force × distance Measured in Joules Is the transfer of energy into

or out of a mechanical system If 40 N of force is applied over

3 m, how much work is done? W = 40 N × 3 m = 120 Joules

Work

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Power = work ÷ time The rate at which work is done.

Measured in watts If Joe uses 400 Joules of work in 40 seconds, how much power did he use?

P = 400 J ÷ 40 sec = 10 watts

Power

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Kinetic energy = ½ the mass times the velocity squared.

Energy of motion – the faster it is moving, the more Ek it has.

If the velocity is doubled, the kinetic energy is multiplied by 4.

If a 3 kg ball is moving at 2 m/s how much kinetic energy does it have?

Ek = ½ mv2 = .5×3×2×2 = 6 Joules

Ek = ½ mv2

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Potential energy = mass × gravity × height Stored energy Energy of position – the higher an object,

the more potential energy it has. Molly has a mass of 60 kg, and is 40 m off

the ground. How much potential energy does she have?

Eg = mgy = 60 × 9.8 × 40 = 23520 Joules

Eg = mgy

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Electrical – anything you plug in, power lines

Nuclear – fission and fusion of atoms Chemical – in foods and fuels Radiant – anything that gives light aka

Electromagnetic Thermal – anything that gets hot Mechanical – (Eg and Ek) Motion and

position of objects.

6 forms of Energy