Question

a 75 watt light bulb is left on at your house over the weekend (48 hours) what volume of water must fall off the 40m high john hart Dam in campbell river to power the light bulb

Answer 1

First, it is necessary to calculate the energy consumed by the bulb during the weekend:


`P = (E)/(t)\ \to\ E = P\cdot t = 75\ W\cdot 48\ h\cdot (3\ 600\ s)/(1\ h) = 1,296\cdot 10^7\ J`

(It is important to express time in seconds).

The energy associated with water is gravitational potential energy and we can write this type of energy depending on volume of water:


`E = m\cdot g\cdot h\\ \rho = (m)/(V)\ \to\ m = \rho \cdot V\\ E = \rho \cdot V\cdot g\cdot h`

Clearing volume in the previous equation:


`V = (E)/(\rho \cdot g\cdot h) = (1,296\cdot 10^7\ J)/(10^3(kg)/(m^3)\cdot 9,8(m)/(s^2)\cdot 40\ m) = \bf 33\ m^3`