# Working out reaction forces in moments

Watch
Announcements
#1
So i’m working through a few moments exam questions and i’ve noticed when e.g working out reaction forces and working with weight sometimes the weight is X 9.8 but others it’s left in newtons and i’m confused when to add the g and when to leave in newton’s. Like for 9a) i did 200g but the mark scheme only used 200 so they ended up getting 125N and i ended up getting 1225.
0
4 weeks ago
#2
I am not actually sure how to answer the questions, but g has the units of an acceleration and N has the units of a force. You are most likely getting muddled up somewhere on this point.

EDIT:

Okay, so the first one, take the moments about point A and assume the weight (a force) of the beam acts downwards at its center.

Then assuming the beam is in equilibrium and not rotating, take moments about point A with clockwise being positive. You have:

The numbers in brackets are the distances in meters and both 200 and C are forces with the unit N. C must therefore be a force in units and you get 125N.
Last edited by 0le; 4 weeks ago
0
X

new posts
Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

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

### Poll

Join the discussion

#### Are you travelling in the Uni student travel window (3-9 Dec) to go home for Christmas?

Yes (107)
28.08%
No - I have already returned home (50)
13.12%
No - I plan on travelling outside these dates (73)
19.16%
No - I'm staying at my term time address over Christmas (39)
10.24%
No - I live at home during term anyway (112)
29.4%