1) The current in an electromagnet connected to a 240-V line is 12.8 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no more than 7.5 celcius degrees?
2) what is the efficiency of a 0.5 hp electric motor that draws 4.4A from 120V line?
2007-10-01 05:59:48 · 3 answers · asked by eri 1 in Science & Mathematics ➔ Physics
1. first thing find the heating effect in watts or Joules or BTU's
240* 12.8 = 3072 watts or 3.072 KW now convert that to joules or BTU which you what to work in. Then find the cooling coefficient of water, Then divide that by the heating effect of the power applied.
2. 746W = 1 hp. 0.5hp = 373 W
373W / 120V = 3.108 amps
3.108 / 4.4 = .706
% of efficiency = 0.706 * 100
% efficiency = 70.6% eff. pretty well in the ball park of a single phase 120V motor. Reason three phase power is a lot better.
2007-10-01 09:53:40 · answer #1 · answered by JUAN FRAN$$$ 7 · 0⤊ 0⤋
enable m be the mass of the vehicle, V its very final velocity, t the time wherein its velocity will improve from 0 to V, P the mandatory customary potential, then the artwork-kinetic potential theorem tells us that we would desire to constantly have mV^2/2=Pt (a million) and so P=mVV/2t (2) remodel the fee in m/s, introduce the corresponding values in (2) as a manner to acquire P in joule/s. Your pocket pc will do the activity.
2016-10-10 02:49:39 · answer #2 · answered by ? 4 · 0⤊ 0⤋
OMG I took physics here at the college. I HATED this class! You should drop it and take something better. This class is a pain and keeps you very stressed. :(
2007-10-01 06:03:19 · answer #3 · answered by Tim James 1 · 0⤊ 0⤋