don't understand force exerted by A on B

dasda

Hey, I need help with the question. I got the acceleration to be (3/8)G

(edited 5 years ago)

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Reply 1

Reply 2

Original post by dasda

Hey, I need help with the question. I got the acceleration to be (3/8)G

Work out the tension in the rope.

Now consider the block B. It has its own weight acting down. It has the reaction force acting up on it (this is just going to be the same as the tension). It has the force exerted by A acting down on it.

Since B is accelerating at 3/8 g we have that the following must hold due to Newton's 2nd Law:

(Weight) + (Force Exerted by A) - (Tension) = (Net Force on B given its acceleration)

(edited 5 years ago)

Reply 3

ghostwalker

Original post by RDKGames

Since B is stationary in the frame of reference of the scale pan, then the vertical forces must balance. I.e.

(Tension) = (Weight) + (Force Exerted by A)

Don't think that's corrrect as the frame of reference is accelerating.

Reply 4

dasda

Original post by ghostwalker

Don't think that's corrrect as the frame of reference is accelerating.

do we use F=ma. Im struggling with these kind of questions

Reply 5

dasda

Original post by RDKGames

Work out the tension in the rope.

Now consider the block B. It has its own weight acting down. It has the reaction force acting up on it (this is just going to be the same as the tension). It has the force exerted by A acting down on it.

Since B is stationary in the frame of reference of the scale pan, then the vertical forces must balance. I.e.

(Tension) = (Weight) + (Force Exerted by A)

The mark scheme shows 2g-reaction force of a = 2a

Reply 6

username4313572

I think it must be in equilibrium because it says 'sits'

Reply 7

username4313572

or am i being stupid
gimme a min, im trying to solve it :P

Reply 8

dasda

no I think its moving

Reply 9

username4313572

what is the answer?

Reply 10

username4313572

I dont want to completely embarrass myself before I say my answer :rofl:

Reply 11

dasda

12.25

Reply 12

dasda

Original post by Serenity-M

I dont want to completely embarrass myself before I say my answer :rofl:

Don't worry. I hate these types of questions

Reply 13

username4313572

hmmmmmm

Reply 14

username4313572

ohhhhh ok. Lemme keep trying :rofl:

Reply 15

Gent2324

resolve the force parallel to the slope, and resolve for the pan and mass.
for the slope its T - component of gravity = 5a, for the mass and pan its 7g - T = 7a
use that to calculate acceleration, then you know that for A, using F=ma, 2g - F = 2a, since you know have A you can solve.