C&G 202 Question

jonnymc11 · Jun 12, 2008

A building hoist is to be used to raise sixty 50kg bags of cememt to the top of a 100m high buliding in 1 minute. Assuming the acceleration due ti gravity would be 10m/s(2), the size of the hoist motor would be:

A- 10kW

B- 50Kw <--------- correct answer, BUT HOW!? please

C- 60Kw

D 100Kw

I thought it may have been:

wd(work done)-F=mg

therefore f X d

but still no clue....

mikey-c · Jun 12, 2008

Power = work / time

Work = force x distance

Force = mass x gravity (in this case)

So...

Power = (mass x gravity x distance)/ time

= (60x50x10x100)/60

= 50 000 W or 50kW

Mr Sworld · Jun 12, 2008

Thank god I don't have to do those anymore! :^O

SPECIAL LOCATION · Jun 12, 2008

Thank god I don't have to do those anymore! :^O

Ditto that Mr S!.....

Indeed.. DOUBLE BLOOMIN DITTO !!!

That is one of of the bits of me electric training that I don't miss at all:^O:^O

All the best to all of you guy's out there still sloggin through the number crunching!

Keep at it lad's....

There is light at the end of the tunnel eventually, don't give up!

jonnymc11 · Jun 13, 2008

phwoarrrr, now hats a beat of an equation to remember

still cant suss it though

mikey-c · Jun 13, 2008

Its just remembering the 3 equations (used in your question) and slowly putting in the know values. Then working your way to the answer.

You need to find the power, so start with p = work/ time

You have the time, 1 minute = 60 seconds

Need to find work done, which is force x distance

You have the distance, 100m

Need to find the force, = mass x gravity

Mass is 60 bags of 50kg. Gravity is 10 m/s2

Hope thats has helped a bit. Write out the calcs on a bit of paper, might look a lot clearer. Dont be discouraged

It took me ages to get the difference between bonding and earthing. And I still dont know the blue and cream fire extinguishers

.