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Where is the normal contact force acting on C ?

thegoldennugget

For part B of this question .

Here is their diagram of the scenario.

Screenshot 2021-01-18 at 20.04.46.png

Surely C would have a normal contact force acting on it ?

Screenshot 2021-01-18 at 20.07.17.png

Thanks.

(edited 3 years ago)

Reply 1

username3477548

Original post by thegoldennugget

For part B of this question .

Here is their diagram of the scenario.

Screenshot 2021-01-18 at 20.04.46.png

Surely C would have a normal contact force acting on it ?

Screenshot 2021-01-18 at 20.07.17.png

Thanks.

i may be wrong, but im pretty sure you can ignore that force because there's an equal and opposite force downwards of the plank on the pivot as well? so they can cancel out

edit: im quite sure my explanation is wrong lol but im not sure whats wrong. if someone understands this pls could they lmk aha :smile:

(edited 3 years ago)

Reply 2

username5586164

Yes, C will have a normal contact force acting on it

Reply 3

mqb2766

Original post by thegoldennugget

For part B of this question .

Here is their diagram of the scenario.

Screenshot 2021-01-18 at 20.04.46.png

Surely C would have a normal contact force acting on it ?

Screenshot 2021-01-18 at 20.07.17.png

Thanks.

The question is about forces acting on the plank.
Forces on other objects are irrelevant.

Reply 4

thegoldennugget

Original post by mqb2766

The question is about forces acting on the plank.
Forces on other objects are irrelevant.

You are a beast, thanks . I made a rookie mistake there.

Reply 5

thegoldennugget

Original post by mqb2766

The question is about forces acting on the plank.
Forces on other objects are irrelevant.

Interesting. I've been analysing this scenario for some time, and I am still confused.

The gravity of C acts on C , but C is at equilibrium and in contact with the rod. The gravity is not a force pair with the contact force exerted on C. So what force is causing that contact force to act on C ?

Reply 6

mqb2766

Original post by thegoldennugget

I'm confused. Are you still analysing the plank or the plank/C pair or what ...?
The gravity of C means what?

I'm guessing that you're trying to consider the forces on C? If so, there would be a downwards force due to the (partial) weight of the plank and an upwards force on the base of C due to whatever it rests on. That upwards force would be equal to the downwards partial plank weight + the weight of C as C is in equilibrium.

Alternatively, if you're concerned that the plank centre of mass (com) isn't directly above C, then resolve vertical forces and/or take moments for the plank to find the component of the plank weight pressing down on C. The weight component of the com pressing down on each support depends on the ratio of the distances of the com from the supports

If that's not what you mean ...

(edited 3 years ago)

Reply 7

username5586164

Original post by thegoldennugget

For part B of this question .

Here is their diagram of the scenario.

Screenshot 2021-01-18 at 20.04.46.png

Surely C would have a normal contact force acting on it ?

Screenshot 2021-01-18 at 20.07.17.png

Thanks.

If this is M1 yOu can just assume the weight of the plank to act at the centre of the plank since it is uniform. So the downward force ON THE PLANK at C is zero.