Chapter 5 Review

Work is force x distance

Only the force parallel to thedisplacement applies to the work

Pulling a box

Fpull = 20N

angle = 30°30°

mass = 15 kgpulled 8 m = .12

Label and calculate all forces

Fpull = 20N

Fpullx = cos30°(20N) = 17.3N

Fpully = sin30°20N = 10N

mg = -147.2N

N = 137.2Nf = -16.5N

Calculate the work done by the pulland friction

Wpull = Fxd = 138.4J

Wf = fd = -132J

Potential Energy is energy of position

GPE = mgh affected by height

EPE = ½kx2

affected by distance squeezed or pulled

k is the spring constant

Kinetic Energy is energy of motion

KE = ½mv2

affected by velocity

if I triple the speed of somethingwhat happens to it’s KE?

Mechanical Energy is PE + KE

MEi = MEf if there is no friction

if there is friction, some KEis changed to heat and lost

40 J of work is done toraise the ball of a pendulum

parallel to the ground30°

If it is released how much KE,PE and ME will it have after 30°?

At its lowest point, how much KE,PE and ME does it have?

½h

½h

10 m

3 m/s

What will the wagon’s speedbe at the bottom of the hill?

KEi + PEi = KEf

½mv2i + mghi = ½mv2

f

v2f = v2

i + 2ghi

vf = 14.3 m/s

5 kg

A 5 kg block is pushed 20 cmagainst a spring with a springconstant of 240 N/m

What is the stored elastic potential energy?

EPE = ½kx2 = ½(240N/m)(.2 m)2 = 4.8 J

If released, what is the velocity of the block, as it comesoff the spring?

KE = EPE = 4.8 J = ½mv2 v = 1.39 m/sIf 4 N of frictional force is acting between the floor andblock, what distance will the block go?

W = KE = f d d = KE / f = 4.8 J / 4 N= 1.2 m