CH 8 Flashcards
What is work?
FORCE X DISTANCE (in the direction of the applied force). Measured in JOULES
If you drag a block 20m with 5N or force, how much work did you do?
100 newton meters, or 100 JOULES
IF WORK=FORCExDISTANCE, then DISTANCE=
WORK/FORCE
IF WORK=FORCExDISTANCE, then FORCE=
WORK/DISTANCE
If you do 10 joules of work over 5 meters, how much force?
WORK/DIST= FORCE so 10 Joules/ 5 meters = 2 NEWTONs
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
What is POWER? (two ways)
WORK/TIME or FORCE*DISTANC/TIME. It measures the rate of work, how fast you can do the work
What is ENERGY?
Ability to do work. Like stored work.
What are the units of ENERGY?
JOULES - think of it as “work waiting to be done” or “stored work”
How is work different from energy?
WORK is being done, Energy is work waiting to be done, like a battery wating to be used.
How is work different from power?
Work is force*distance, and power is an amount of work per unit of time. It is work/time. Power is a RATE OF DOING WORK, basically, how fast you can do the work.
What is the unit of work we use?
JOULE (newton*meter)
What is the unit of power we use?
WATT (joule/sec) or (newton*meter/second)
What is the unit of energy we use?
JOULE (newton*meter)
Explain FORCE units two ways
Newton or kg*m/s2
Explain POWER units three ways
WATT or joule/s or kg*m2/s3
Explain WORK units three ways
JOULE, or Nm, or kg*m2/ s2
What is potential energy?
mgh- non-moving stored energy. from HEIGHT.
What is kinetic energy?
one half mass velocity squared. MOVING energy.
You lift 8kg up 5 meters, How many JOULES?
400 Joules
You lift 8kg up 5 meters in 4 seconds, how many WATTS of power?
100 watts
You lift 8kg up 5 meters in 20 seconds, how many WATTS of power?
20 watts
there are ______ of FORCE, ____ of WORK ,______ of POWER and _____ of ENERGY
NEWTONS of force, JOULES of work, WATTS of power and JOULES of energy
EQN relating change in PE to change in KE
mg(delta h)= 1/2 m(delta v)2
Conservation equation
PEo+KEo = PEf +KEf or mgh+1/2 mv2 = mgh + 1/2 mv2 (notice the mass can cancel if it doesn’t change)
How much energy in a 25kg block 4meters high?
PE= mgh = 25104 = 1000 J
How much energy in a 4kg block traveling 3 m/s
KE = mv2/2 = 4*3^2 / 2 = 36/2 = 18 J
How much power if you move 50 kg 20 meters in 10 seconds?
P = Fd / t = 50*20/10 = 100 WATTS
WATTS measure ____
Power
NEWTONS measure____
Force
JOULES measure _____
Work and Energy
What are the two energies we talk about in this unit?
Potential (height) and Kinetic (speed)
