# multiple choice help

Thread starter 4 years ago
#1
Hi

an help would be appreciated

an electric motor of input power 100w raises a mass of 10kg vertically at a steady speed of 0.5ms. What is the efficiency of the system
0
4 years ago
#2
(Original post by GG16)
Hi

an help would be appreciated

an electric motor of input power 100w raises a mass of 10kg vertically at a steady speed of 0.5ms. What is the efficiency of the system
P = WD / t = F x (D / t) = F x v

Can you work out the answer from here?
0
4 years ago
#3
(Original post by GG16)
Hi

an help would be appreciated

an electric motor of input power 100w raises a mass of 10kg vertically at a steady speed of 0.5ms. What is the efficiency of the system
Hello there,

You should be able to calculate the output power as using the applied force (equal to the object's weight in this case) and the speed of ascent. You should use the equation . You can then find the efficiency by dividing this by the input power and if they want it as a percentage, multiply it by .

I hope that this has been helpful.

Smithenator5000.
0
4 years ago
#4
(Original post by GG16)
an electric motor of input power 100w raises a mass of 10kg vertically at a steady speed of 0.5ms. What is the efficiency of the system
The efficiency is the useful work output divided by the input power. We have the input power of 100W. What's the useful work output?

(You should get an answer of somewhere close to 50%)
0
4 years ago
#5
(Original post by GG16)
Electric motor of input power 100 W raises mass of 10 kg vertically at steady speed 0.5 ms^-1. What is the efficiency of the system?
Power of mass is its weight x speed (10 x 9.81 x 0.5)
Took 100 W of electrical input power to attain that.
Efficiency = (Output/Input) x 100% = 49.1%
0
7 months ago
#6
why did you times by 9.81, i dont understand
0
7 months ago
#7
(Original post by Subhawk)
why did you times by 9.81, i dont understand
The thread is 4 years old...

Power = Force * Velocity
Get Force (weight) and you know velocity
Hence have the power actually needed to lift the object (the output)
You're given the input
Efficiency is input/output * 100

You need 9.81 to calculate the weight (force)
0
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