A 120 kg piano is being lifted at a steady speed from ground level straight up to an apartment 18.0 m above the ground. The crane that is doing the lifting produces a steady power of 400 W. How much time does it take to lift the piano?
2007-01-08 09:33:01 · 3 answers · asked by Lucy 1 in Science & Mathematics ➔ Physics
mgh=120*10*18=21600j
p=w/t
w=mgh
t=w/p
t=21600/400=54s
2007-01-08 09:42:29 · answer #1 · answered by a 3 · 0⤊ 0⤋
Power is energy/time. Work is also energy.
So, calculate the potential energy stored in the lifted piano:
PE = mgh
then equate it to the power*time:
PE = power*time
and solve for time
time = PE/400
You'll need to convert some units. Note that 1 watt = 1 joule/sec
2007-01-08 17:39:11 · answer #2 · answered by modulo_function 7 · 0⤊ 0⤋
mass = 120 kg
height = 18 m
Potential = 400 W
time
P = (mgh)/t
400 W = (120 kg * 18 m * 9.8 m/s2)/t
400 W = 21168 Joules/ t
t= 21168 Joules/ 400 W
t= 52.92 sec
2007-01-08 18:59:25 · answer #3 · answered by Jose 2 · 0⤊ 0⤋