Chapter 5 Review

Work is force x distance Only the force parallel to the displacement applies to the work

Calculate the work done by the pull Fpull = 20N Pulling a box N = 137.2N f = -16.5N Fpull = 20N Fpully = sin30° 20N = 10N 30° angle = 30° Fpullx = cos30°(20N) = 17.3N mass = 15 kg mg = -147.2N Label and calculate all forces pulled 8 m m = .12 Calculate the work done by the pull and 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

if I triple the speed of something Kinetic Energy is energy of motion KE = ½mv2 affected by velocity if I triple the speed of something what happens to it’s KE?

Mechanical Energy is PE + KE MEi = MEf if there is no friction if there is friction, some KE is changed to heat and lost

raise the ball of a pendulum 40 J of work is done to raise the ball of a pendulum parallel to the ground 30° ½h If it is released how much KE, PE and ME will it have after 30°? ½h At its lowest point, how much KE, PE and ME does it have?

What will the wagon’s speed be at the bottom of the hill? 3 m/s What will the wagon’s speed be at the bottom of the hill? KEi + PEi = KEf ½mv2i + mghi = ½mv2f 10 m v2f = v2i + 2ghi vf = 14.3 m/s

against a spring with a spring constant of 240 N/m A 5 kg block is pushed 20 cm against a spring with a spring constant of 240 N/m 5 kg 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 comes off the spring? KE = EPE = 4.8 J = ½mv2 v = 1.39 m/s If 4 N of frictional force is acting between the floor and block, what distance will the block go? W = DKE = f d d = DKE / f = 4.8 J / 4 N = 1.2 m