Question

A 15-kilowatt motor is used to hoist an 800 kg bucket of concrete to the 20th floor of a building under construction to height of 90 m. assuming no energy is lost along the process, how much time is required?

Answer 1

$work done, mgh=power (P)\times time(t)$

$mgh=P\times t$

$800\times9.8\times90=15\times1000 \times t$

$t=(800\times9.8\times90)/15000=47.04seconds$