CH 7 and CH 8 Flashcards Preview

2019 PHYSICS fall > CH 7 and CH 8 > Flashcards

Flashcards in CH 7 and CH 8 Deck (62)
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1

What is momentum equation?

p=mv (my pigeon is from martha's vineyard)

2

What are the units of momentum?

no special name. just kg*m/s

3

If two objects have the same velocity, the one with the larger mass has _____ momemtum

larger

4

if two objects have the same mass, the one with less velocity has _____ momentum

less

5

As velocity increases, momentum _____

increases

6

What is impulse? what is the symbol?

Change in momentum, or FORCE*TIME or MASS*delta V.
the symbol is DELTA P
(a force over an amount of time changes momentum)

7

what are the units of impulse?

no special name. same as momentum. kg*m/s

8

Give a clear example of impulse:

Since the mass generally stays the same.. you can view impulse as the thing that changes the velocity of an object. An impulse slows an object down, or speeds it up. Yes, force changes it.. but impulse measures how much. A force for 5 seconds changes it a little, the same force for an hour changes it more. Impulse helps us see the difference.

9

What is "FAT MAV?"

F delta T = m delta v (force * change in time = mass * change in velocity)

10

F = ma can be changed to what?

to FAT MAV: change the a to (delta v / delta t) so you get: F = m (delta V / delta T)
this is another version of fat mav.

11

What does "conservation of momentum" mean?

Momentum before = momentum after

12

What are the three conservation of momentum equations we use in this class? (along with the situations

mv+mv= mv + mv (separate before and after). (m+m)v = mv + mv (stuck before). mv+mv= (m+m)v (stuck after)

13

What changes the momentum of an object?

Applying a force over an amount of time (WHICH IS IMPULSE!!). Impulse changes momentum.

14

mv = Ft what does this say?
(what is delta t?)

Generally used when something crashes. momentum before = impulse (because all of the momentum is lost in a crash). Mass times velocity before = Force (time).
delta t is always just t. it is positive. time is not negative.

15

What is an elastic collision?

When all KINETIC energy is preserved (we solve problems like this, but in reality, energy is usually lost in sound and heat)

16

What is an inelastic collision?

When some momentum, some energy is lost through heat, sound, etc (stuck together)

17

What types of collisions do we usually consider when solving problems in class?

We assume they are elastic collisions (similar to how we often ignore friction).

18

Which causes more impulse, a 1kg ball hitting you at 10m/s and falling, or bouncing off your head and traveling back at 5 m/s?

A ball bouncing causes more of an impulse. Impulse is change in momentum. The ball that stops velocity only changes 10m/s (from 10 to 0), the bouncing ball goes from +10m/s to -5m/s, an overall change of 15m/s. The more the velocity changes, the more the momentum changes, which is a larger impulse!

19

When a cannon is fired, explain how momentum is preserved.

mv(cannon) + mv(ball) before is ZERO. It has to be zero after, so the momentum the cannon moves must be opposite the momentum of the ball to cancel it out, so they must have the same magnitide. so after the cannon fires, MV (cannon) = MV (cannonball).

20

How are FORCE and MOMENTUM different?

Force = mass (acceleration) where Momentum = mass (velocity)

21

What is work?

FORCE X DISTANCE (in the direction of the applied force). Measured in JOULES
W=F*D
(The Weiner is a Friendly Dog)

22

If you drag a block 20m with 5N or force, how much work did you do?

100 newton meters, or 100 JOULES

23

IF WORK=FORCExDISTANCE, then DISTANCE=

WORK/FORCE

24

IF WORK=FORCExDISTANCE, then FORCE=

WORK/DISTANCE

25

If you do 10 joules of work over 5 meters, how much force?

WORK/DIST= FORCE so 10 Joules/ 5 meters = 2 NEWTONs

26

If you do 20 joules of work using 5N of force, how far did you go?

WORK/FORCE=DISTANCE so 20 joules/ 5 newtons= 4 meters

27

If you are holding a barbell still, is there any work being done? is there any force?

No work, because there is no distance. There are forces, but no NET force. The forces are all balanced. The force your arm is holding it is equal to the force of gravity, so it isn't moving.

28

What is tricky about force, work and direction?

In order for work to be done, it has to happen in the SAME DIRECTION of the force applied. So if you walk across a room holding a barbell, no work is done on the barbell because it doesn't move UP.

29

What is POWER? (two ways)

WORK/TIME or FORCE*DISTANC/TIME. It measures the rate of work, how fast you can do the work

30

What is ENERGY?

Ability to do work. Like stored work.