# Chapter 7 - Forces and Energy Flashcards

## Work, Energy, and Power, Hooke's Law, and Dimensional Analysis. May the force be with you for this chapter...

What is work done?

Work done (in Joules) is force x distance, when the direction of the force is in the same distance as the force.

Wd (J or Nm) = F x x

or

Wd (J or Nm) = ∫ 0 to x Fdx

or

Wd (J or Nm) = Fxcos(θ)

Define Power, from:

- a force, and speed.

- work done and time taken.

The power of a constant force F moving at a steady speed v is equal to F x v, where power is in W (watts), force in N, and speed is ms⁻¹.

If F or v are variable, F x v gives the power at that particular instant.

The average power of an ‘engine’ is defined as work done ÷time taken, where work done is in J (joules) and time taken in s.

What is the kinetic energy of a body with mass and velocity v?

The kinetic energy of a body with mass m and velocity v is equal to ½mv².

What is the gravitational potential of a body?

The gravitational potential energy of a body with mass m at height h (gravity is g) is equal to mgh.

What is Hooke’s law?

Hooke’s law gives T = (𝛌/l)x, where T is tension, lambda is the modulus of elasticity, l is the natural length, and x is extension.

How do you find the elastic potential energy stored in a spring/string?

What are the three fundamental dimensions?

The three fundamental dimensions are:

Mass, M

Length, L

Time, T

State the principle of conservation of mechanical energy in relation to Kinetic Energy and Gravitational Potential Energy.

The Principle of Conservation of Mechanical Energy says that the total mechanical energy (the sum of KE and GPE) of a system remains constant, provided no work or energy is lost to friction or impacts.

Loss of GPE = Gain in KE + Work done against air resistance, where GPE is mass x gravity x distance (KG, g, m), Kinetic energy is ½mv², and Air Resistance is Force x Distance.

State the principle of conservation of energy, and therefore, state the equation for loss of GPE.