You are Here: Home >< Physics

# Physics Crane Question watch

1. A crane is lifting a car of load 850 kg. It lifts the car 12m in 40s. The crane has 60% efficiency. Find the input power of the crane. I had this question for my mock. I used P=F/v but unsure. The first part of this question was to find T. Please help thanks.
2. Refer to post below.
3. There is another formula for power, which is power = work done/time taken

First work out the amount of gravitational potential energy car will have when fully lifted, which is worked out by: G.P.E (gravitational potential energy)= mass * gravitational field strength * height
so...G.P.E = 850 * 9.81 * 12 = 100062 Joules

Then it says crane has 60% efficiency, so the G.P.E equivalent is the 60% of total energy inputted, so you work out what 100% is, which is done by:
(work out 40%)..(100062/3)*2=66708
When you add 40% to 60%, you get 100%, so 100062 + 66708 = 166770 Joules

Then use the power equation
Power = 166770/12 = 4169.25 W required as input

Can you clarify what T is? Is it tension?
4. (Original post by Outofthisworld)
A crane is lifting a car of load 850 kg. It lifts the car 12m in 40s. The crane has 60% efficiency. Find the input power of the crane. I had this question for my mock. I used P=F/v but unsure. The first part of this question was to find T. Please help thanks.
Just out of curiosity, is this for mechanics maths or physics?
5. (Original post by G.Y)
Just out of curiosity, is this for mechanics maths or physics?
Physics since you had to use power formula and the thread title also says physics
6. Yes T was tension, I got the same answer as you but I did P=Fv or work done/time then divide by 0.6. But I like your explanation of using G.P.E, it's makes more sense cause we know that the crane did work against gravity to bring the car to 12m.
Thanks!
7. Yes, I think I got the answer. It was 4 mark so I was thinking it's too simple and so many marks just for this question. But I got this .
8. (Original post by neluxsan)
Physics since you had to use power formula and the thread title also says physics
Lol whoops

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 13, 2018
Today on TSR

### He broke up with me because of long distance

Now I'm moving to his city

### University open days

1. Norwich University of the Arts
Thu, 19 Jul '18
2. University of Sunderland
Thu, 19 Jul '18
3. Plymouth College of Art