I need help on a mechanics 2 question

I have done part a and got acceleration to be 4.48ms^-2
Need help on part b

My working out:

The diagram I used:

My working out:

The diagram I used:


Part a working out: https://www.thestudentroom.co.uk/attachment.php?attachmentid=610002&stc=1&d=1483978356

attempt at b working out: https://www.thestudentroom.co.uk/attachment.php?attachmentid=610004&stc=1&d=1483978400

You need to also consider the work done by friction

I haven't checked all your working but I think you've made a mistake when considering the gravitational potential energy.

Remember that the gain in GPE is equal to $mgh$ where $h$ is the vertical distance moved. But you need to work out the distance moved up the slope.

Does that help?

When B descend down by 1m, does A also move 1m up the slope?

K.E lost = mgh gained - work done by the frictional force ?

When B descend down by 1m, does A also move 1m up the slope?

yeah thats right


I got taught loss GPE + loss KE = work done by friction



I can try to answer it if you give me 5 mins, do you have the answer with you?

Yes but is that 'h' in the formula mgh?

yes that's h - the vertical distance moved

Here's what I did, see if you can follow it and get the answer:

Starting from Loss KE + Loss GPE = Work done by friction

I let d be the distance it moves up the slope. Since I let d be the distance up the slope, my loss in GPE will be negative
Work done by friction is d mu R.

Remember that the vertical height the object moves if it goes d up the slope is dsin theta vertically