# How would the mass at B work in this moments question?

Usually in moments questions it justs say a mass it attached at a certain point or whatever but in this one a string is attached as well. Does this mean there will be a tension force that i have to use in the question or do i just go about it normally?

(edited 9 months ago)
Original post by 43Explosion
Usually in moments questions it justs say a mass it attached at a certain point or whatever but in this one a string is attached as well. Does this mean there will be a tension force that i have to use in the question or do i just go about it normally?

Not sure why theyve added the fact that its suspended on there, but in equilbrium, the tension in the string must equal mg (so "pull up" the mass) which in turn will "pull down" the rod with a force mg at B. So the mass could equivalently be at B.

So take moments for the rod (about A?) as normal. Its the tension acting on the rod, but its trivially equal to the weight.
(edited 9 months ago)
Original post by mqb2766
Not sure why theyve added the fact that its suspended on there, but in equilbrium, the tension in the string must equal mg (so "pull up" the mass) which in turn will "pull down" the rod with a force mg at B. So the mass could equivalently be at B.

So take moments for the rod (about A?) as normal. Its the tension acting on the rod, but its trivially equal to the weight.

Thank you this makes it easier to understand. The question is from madasmaths so that's probably why it's a bit different from normal
Original post by 43Explosion
Thank you this makes it easier to understand. The question is from madasmaths so that's probably why it's a bit different from normal

I recognised it. Tbh, as its slightly different from normal it should test your understanding. The key thing is that for the rod moments, you only consider forces acting directly on the rod (tension at B ...), so its a reasonable test of that.
(edited 9 months ago)