Exploring Energy Concepts

A 2.5 × 3.5 × 6 in. brick whose density is 120 lb/ft3 slips off the top of a building under construction and falls 69 ft. For g = 32.0 ft/s2, determine the change in gravitational potential energy of the brick, in ft · lbf.

Step 1 of 4:

The density and volume of a brick are given. The brick falls from the top of the newly constructing building. We are going to find the change in gravitational potential energy of the brick. We need to convert the units into SI standard to solve the problem easily.

Volume of the brick V = 2.5 × 3.5 × 6 in3 = 52.5 in3 = 0.00086 m3

The density of the brick ρ = 120 lb/ft3 = 1922.22 kg/m3

Height of the building h = 69.0 ft = 21 m

The acceleration due to gravity g = 32.0 ft/s2 = 9.81 m/s2

Step 2 of 4:

The gravitational potential energy at the top of the building

Where m is the mass of the brick