Work & Energy

Question 1

Define Work

Answer 1

Work is energy transferred by a force

W = Fd (or s) = Fs.cos(theta)

Using Kinematics…

F = ma

therefore W = m • a • d

note*: from Kinematics we know that V_f^{2 =}V_i²+ 2a•d where a=f/m, but f•d = W, so W = 1/2•mV_f² (V_i = 0)

Question 2

What is Kinetic Energy?

Answer 2

Amount of work required to get from V_i to V_f

W = K_E = F•d = 1/2 mV_f² (joules)

Question 3

What is Potential Energy?

Answer 3

P_E= F•d = m•a•d = m•g•h

It is the potential energy to be converted into K_E

for freefall example, conversevation of energy tells us that K_Ei + P_Ei = K_Ef + P_Ef

if you can solve for the potential energy, you can convert this knowledge to work out the velocity at any point!

Question 4

Work-Energy Theorem

Answer 4

W_tot = K₂ - K₁ = ΔK

Question 5

Work done by a varying force or on a curved path?

Answer 5

W = The integral from x₁ to x₂ of F_x.dx

AND

W = The integral from P1 to P2 of Fcos(theta).dl = The integral from P1 to P2 of F_||.dl = The integral from P1 to P2 of F.dl

Question 6

What is the equation to calculate average power?

Answer 6

P_av = ΔW/Δt

Question 7

What are the equations to calculate power?

Answer 7

P = lim(Δt->0).ΔW/Δt = dW/dt

P = F.v