Chapter 5 Test

work

done when a force (F) creates a displacement (s)

work in same direction equation

W = Fs or W = ∆K

work in different directions equation

W = F_lls; W = Fcos(angle)s

work units

SI- J = N * m

CGS- erg = Dyne * cm

BE- ft * lb

work energy theorem

when work is done on something, its kinetic energy changes

work energy theorem equation

W = ΔK; derived from F = ma where a is replaced by (v²-v₀²)/2s

kinetic energy

energy of motion

kinetic energy equation

K = ½ m v²

kinetic energy unit (SI)

J

gravitational potential energy

U; energy of position (energy based on a position above a reference level)

gravitational potential energy equation

U = mgh

gravitational potential energy unit (SI)

J

gravitational potential energy is related to work done by

gravity; W_g = -ΔU becomes W_g = mgh₀ - mgh

spring force

Hooke’s Law; force that opposes the stretching or compressing (restoring force)

spring force equation

F_spring = -k∆x; k is spring constant and ∆x is change in length

spring force unit

N

spring constant

k; changes based on the spring

spring constant unit

N/m

spring potential energy

equal to the work done by spring; W = F * d changes into W = ½kx * x and then to U_spring = ½ k x²

mechanical energy

E, the sum total of kinetic and potential energy

mechanical energy equation

E = U + K

conservative force

a force that does not net work if there is no displacement; ex: gravity

conservation of mechanical energy

if there is no non-conservative work done, mechanical energy is conserved; used for finding final or initial heights or speeds

conservation of mechanical energy equation

E₀ = E; K₀ + U₀ = K + U; ½v₀² +gh₀ = ½v² + gh

non-conservative force

a force that does work independently of the path; ex: friction, air resistance

non-conservative force equation

W_total = W_Nonconsv + W_consv

ΔK = W_NC + W_g

ΔK = W_NC − ΔU

W_NC = ΔK + ΔU

W_NC = (K – Ko)+ (U – Uo)

W_NC = (½m(v²) - ½m(v₀²)) + (mgh - mgh₀)

non-conservative forces and mechanical energy

no non-conservative forces when mechanical energy is conserved

power

P, work done per unit time; average rate at which work is done

power equation

P = work/time = W/t

Power units

Si- Watt = J/s

CGC- erg/second

BE- (ft * lb)/s