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# LPH 105 W15 6:1-3

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## Richard Datwyler

on 18 May 2016

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#### Transcript of LPH 105 W15 6:1-3

With pulleys we say 'count the ropes' and that will decrease the force needed to lift something.
What about the work?
10 kg
How much force is required to lift this block at a steady speed?
If I lift it up by hand 1.5 m how much work would I do?

What is the initial energy? What is the final energy?
If I lifted it up with this block and pulley set up, how much work would I do?
49 N
W=F*D = mg*d =147 J
W=F*D=1/2 mg *2D = 147 J
PE = mgy
PE = 0
PE = mgy = 147 J
f
i
What is the minimum work needed to push a 750 kg car 500 m up a 10 incline (ignore friction)
0
If there was a force of friction having a coefficient of friction being 0.15, what would the minimal amount of work needed to do the same action?
638 KJ
1180 KJ

A 350 kg piano slides 3.0 m down a 20 incline and is kept from accelerating by a man who is pushing back on it parallel to the incline. Determine
a) the force exerted by the man
b) the work done on the piano by the man
c) the work done on the piano by the force of gravity
d) the net work done on the piano.
Ignore friction

1173 N
-3519 J
3519 J
0 J
How much work is required to stop an electron which is moving with a speed of 1.1 x 10^6 m/s
5.5 x 10^-19 J
How much work must be done to stop a 925 kg car traveling at a speed of 45 m/s?
A baseball mass = 145 g traveling 30 m/s moves a fielder's glove backwards 25 cm when the ball is caught. What was the average force exerted by the ball on the glove?
937 KJ
261 N
At an accident scene on a level road a car left skid marks 75 m long. The road was wet and the coefficient of friction was guessed to be 0.30. Determine the speed of the car when the driver slammed on his breaks.
21 m/s
A novice skier starting at rest slides down an icy frictionless 10 degree incline whose vertical height is 100 m. how fast is she going when she reaches the bottom?
44 m/s
What minimum speed must a high jumper leave the ground with in order to lift his center of mass 2.1 m pole and cross the bar with a speed of 0.5 m/s? (ignore any energy in the pole)
6.4 m/s
"Can you show us how an area on a force vs distance graph can help us find the work done by a varying force? "
"How do we figure the angle of the force? (i.e In the last problem on the quiz,"
"I still don't really understand what you meant about how force is 0 if it doesn't moves up or down. "
If a force of 20.0 N is used to lift a box a distance of 2.50 m, how much work was done? (answer should look like '25.1 J')
d=500m
10
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