The Student Room Group

as physics (mechanics) question help needed

A hydraulic jack used to lift a car which has a mass of 1200kg. A mechanic exerts a
downwards force of 400N on the handle of the jack, moving it 80.0cm downwards. As he moves
the handle, the car rises 2.0cm.

Calculate the work done by the 400N force exerted by the mechanic.

I assume it cant be as simple as multiplying 400N by 0.02m because that gives 8 joules to lift the car but idk
The 400N force is on the handle of the jack, not directly on the car.
Reply 2
Original post by mqb2766
The 400N force is on the handle of the jack, not directly on the car.


Yeah i know but since thats the initial force it made me think that might be the way, however its obviously not so a nudge in the right direction would be appreciated.
Original post by strauss333
Yeah i know but since thats the initial force it made me think that might be the way, however its obviously not so a nudge in the right direction would be appreciated.


That was a hint :-). Over what distance (length of path) does the 400N force act? There are not that many distances in the question.

The scenario is similar to a lever.
(edited 1 year ago)
Original post by mqb2766
That was a hint :-). Over what distance (length of path) does the 400N force act? There are not that many distances in the question.

The scenario is similar to a lever.


The ans should be 312 J right?
Original post by Anonymous(
The ans should be 312 J right?


How? Close but ...
Original post by mqb2766
How? Close but ...

Should be 328 right? My bad
Original post by Anonymous(
Should be 328 right? My bad


No. Again, close but ...
While the full question hasnt be posted, it is part of a multipart question, so some of the info isnt relevant for this part.
Its a 2 marker.
(edited 1 year ago)
Original post by mqb2766
No. Again, close but ...
While the full question hasnt be posted, it is part of a multipart question, so some of the info isnt relevant for this part.
Its a 2 marker.


Lmaoo I just read the qs again realised how stupid I was being….
Reply 9
Original post by mqb2766
That was a hint :-). Over what distance (length of path) does the 400N force act? There are not that many distances in the question.

The scenario is similar to a lever.

thanks :smile: I wasnt sure which force and which distance to use. one of the later parts was calculate the efficiency; i just wanted to check that to calculate the work done on the car the force up would need to be 11772 N?
Original post by strauss333
thanks :smile: I wasnt sure which force and which distance to use. one of the later parts was calculate the efficiency; i just wanted to check that to calculate the work done on the car the force up would need to be 11772 N?

Assuming g=9.81 then yes, but really you just want to get the change in GPE so the force is part of that but you should just use GPE directly?
Original post by mqb2766
Assuming g=9.81 then yes, but really you just want to get the change in GPE so the force is part of that but you should just use GPE directly?

yh i used 11772 x 0.02 which gives GPE
Original post by strauss333
yh i used 11772 x 0.02 which gives GPE


Looks good. It might be worth reviewing levers from a work done viewpoint, so something like
https://ecampus.matc.edu/mihalj/scitech/unit1/levers/levers.htm
The key thing is that you multiply the (constant) force by the length of the path (arc) along which it acts.
thanks 🙏🏼

Quick Reply

Latest