Two floors in a building are separated by 4.1 m. People move between the two floors on a set of stairs. (a) Determine the change in potential energy of a 3.0 kg backpack carried up the stairs. (b) Determine the change in potential energy of a person with weight 650 N that descends the stairs.

a) The change in potential energy of a 3.0 kilograms backpack carried up the stairs.

b) The change in potential energy of a persona with weight 650 newtons that descends the stairs is -2665 joules.

Explanation:

Let consider the bottom of the first floor in a building as the zero reference (). The change in potential energy experimented by a particle (), measured in joules, is:

(1)

Where:

- Mass, measured in kilograms.

- Gravitational acceleration, measured in meters per square second.

, - Initial and final height with respect to zero reference, measured in meters.

Please notice that is the weight of the particle, measured in newtons.

a) If we know that , , and , then the change in potential energy is:

The change in potential energy of a 3.0 kilograms backpack carried up the stairs.

b) If we know that , and , then the change in potential energy is:

The change in potential energy of a persona with weight 650 newtons that descends the stairs is -2665 joules.

trig 15.3 cos

5 w for 1hr = 5x60x60 joules=300x60=3000x6=18,000j as total energy conversion. efficiency of bulb needed for radiant to thermal within 18000