# Shared Flashcard Set

## Details

Crawford Semester Exam
2012 Semester Exam Review
26
Physics
12/18/2012

Term
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 Walk away from the origin quickly, gradually slowing down.
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 Constant Speed Away from the start
Term
 displacement
Definition
 Measured in meters   From the start to the finish (not distance which is the entire path)
Term
 Relative to
Definition
 In relation to a reference point   If a bus is moving 20 mph and you walk 1 mph to the front, then you ADD the velocities. If you are walking from the front to the back, you subtract
Term
 Newton's 1st Law
Definition
 Law of Inertia and car crashes   The more mass you have, the more inertia you have.   Inertia determines the ability to make something stop or change its motion. So, it is easier to change the motion of a baby stoller than it is a school bus.   More mass = more inertia
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 Newton's 2nd Law
Definition
 F = m x a   measured in Newtons   If something is falling or the mass is affected by gravity, you can use   W (weight) = m x g   Why? Weight IS a force due to gravity.
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 Newton's Third Law
Definition
 Action and Reaction Pairs   Equal Forces in opposite directions   You hit the wall and it hurts because the wall was hitting you!   If the bug hits a windshield, we are sad that the big died, but the bug put the same force on the windshield that the windshield put on the bug
Term
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Definition
 Object is NOT at rest...look at y axis!   The object is moving at a constant velocity
Term
 What should I study for the semester exam?
Definition
 1. All your old chapter tests that we taped into your notebook 2. The notes on graphing 3. CBA 1 and 2 4. The practice semester exam we did in class yesterday   A lot of the questions are similar or even the same, so please review the old tests and CBAs!!!!!!!!
Term
 1. Which object has a greater inertia? A. 2kg object moving at 6m/s  B. 3kg object moving at 5m/s C. 6kg object moving at 0m/s  D. 7kg object moving at 1m/s
Definition
 D. An object with more mass has more inertia
Term
 Law of conservation of energy
Definition
 Potential has to do with how high something is (GPE = m g h) and Kinetic has to do with how fast something is going (KE = 1/2 m v ^2)   Potential is converted to kinetic as an object falls   The potential at the top is 100% and the kinetic is 0%. By the time the object hits the ground, it is moving the fastest, so its kinetic is now 100% and potential is 0%.
Term
 work
Definition
 work is measured in JOULES   Work = change in kinetic energy   work = force x distance   example: If you walk up the stairs, like in our lab, you walked up a distance of 2.16 meters. We would multiply your force by the distance you went UP from the ground.   What happens if you don't have the force??? Well, you have to do (m x g) to get the force!
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 Work = change in kinetic energy
Definition
 The amount of work you do is equal to the change in kinetic energy.   Let's say you drop a 2 kg ball from rest and by the time it hits the floor it was going 10 m/s.   Work = the change in KE   So you have to calculate the KE initially and then the KE from when it hits the ground and then subtract.
Term
 Law of conservation of momentum
Definition
 momentum before = momentum after   the velocity may change when something is hit that was originally at rest, but their momentum will never change
Term
 With projectile motion, when do I use   v = d/t
Definition
 ...when you are solving for a horizontal throw!
Term
 With projectile motion, when do I use: d = vit + 1/2 at2 converted to: y = 1/2 gt2
Definition
 We use these formulas when we want to know how far down something has fallen or how high the cliff is.
Term
 When do I use "g" instead of "a"?
Definition
 If something is falling or being dropped, gravity is a factor, so you would use g = 9.8 instead of solving for "a".   For example, if you are lifting a 20kg dog 3 meters and want to know the work:   w = f x d   w = m x g x h   w = 20 kg x 9.8 x 3 m
Term
 A 5kg box is being pushed with a force of 20 N up a 10m ramp that is 4m off of the ground. How much work would be done to lift the box to the top?
Definition
 Since work = force x distance,   W = 20 N x 4 m = 80 J   You don't use the mass because we already know the force (and don't need to do f = m x g to get it) and we want to know how high the box was lifted, not how long it was pushed, so we don't use the 10 m.
Term
 A resultant vector represents the sum of two or more vectors. If Juan walks 200 m east and then 600 m west, What is his displacement (including direction)?
Definition
 400 m west   Why?   He is walking in two different directions, so you subtract.
Term
 Alex throws a football off the top of the school to a friend below. He throws the ball at 2 m/s. The school is 10 m high. How much time does it take for the ball to hit the ground?
Definition
 Remember, time to launch (horizontally) equals time to drop (vertically).   So, you can use y = 1/2 g t2   10 = 1/2 (9.8) t2   t2=2.04   square root both sides   t = 1.43 s
Term
 What is the impulse of a 10 N force acting westward on a car for 5 seconds?
Definition
 Impulse = force x time   10 n x 5 seconds = 50 N s westward
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 When friction is applied to an object in motion, what does the kinetic energy convert to as it slows down?
Definition
 Friction can cause energy to be converted to heat.
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