multiple choice help

Watch this thread
GG16
Badges: 10
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#1
Report 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
reply
DanielDaniels
Badges: 14
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#2
Report 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
reply
Smithenator5000
Badges: 9
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#3
Report 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  P = Fv . You can then find the efficiency by dividing this by the input power and if they want it as a percentage, multiply it by  100\% .

I hope that this has been helpful.

Smithenator5000.
0
reply
RogerOxon
Badges: 21
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#4
Report 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
reply
Physics Enemy
Badges: 19
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#5
Report 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
reply
Subhawk
Badges: 1
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#6
Report 7 months ago
#6
why did you times by 9.81, i dont understand
0
reply
Callicious
Badges: 22
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#7
Report 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
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Year 12s - where are you at with making decisions about university?

I’ve chosen my course and my university (26)
27.37%
I’ve chosen my course and shortlisted some universities (31)
32.63%
I’ve chosen my course, but not any universities (10)
10.53%
I’ve chosen my university, but not my course (3)
3.16%
I’ve shortlisted some universities, but not my course (5)
5.26%
I’m starting to consider my university options (14)
14.74%
I haven’t started thinking about university yet (4)
4.21%
I’m not planning on going to university (2)
2.11%

Watched Threads

View All