Unit 1-3 Review 1

Calculate acceleration, distance, velocity & time Read position-time, velocity time graphs Define velocity, speed and acceleration 2

 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 3

 If Jill drives at 30 m in 6 seconds. What is her velocity?  V = D ÷ t  30 m ÷ 6 sec  5 m/s 4

 If Chase drives 30 m/s for 7 seconds, how far has he gone?  D = V × T  30 m/s × 7 sec  = 210 m 5

 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 6

 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 7

 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. 8

 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. 9

 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 10

 Change in velocity ÷ time  Slope of a velocity-time (v-t) graph  Speeding up  Slowing down  Changing direction  If an object does not accelerate, it moves at a constant velocity 11

 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) 12

F = ma Net force Newton’s Laws Momentum 13

 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 14

 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. 15

 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 16

 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) 17

 An object in motion or at rest will stay in motion or at rest unless acted on by an unbalance (net) force.  Law of Inertia  Objects want to keep doing what they are doing. 18

 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. 19

 For every action force, there is an equal and opposite reaction force.  Action-reaction forces are equal in size and opposite in direction. 20

 P = mv  What is the momentum of a 5 kg rock moving at 2 m/s?  P = 5 kg × 2 m/s  = 10 kg  m/s 21

W = FD P = W/t Ek = ½ mv 2 Eg = mgy 6 forms of energy 22

 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 23

 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 24

 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 mv 2 =.5×3×2×2 = 6 Joules 25

 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 = Joules 26

 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. 27