Minimum Force such that box m does not slide down

AI Thread Summary
The discussion revolves around calculating the minimum force required to prevent a smaller box (m) from sliding down a larger box (M) under the influence of gravity and friction. The calculations indicate that an acceleration of 49.05 m/s² is necessary for box m to remain stationary relative to box M, which is significantly higher than the provided acceleration of 2.0 m/s². Participants express confusion over the exercise's wording and the unrealistic nature of the given acceleration. Suggestions include assuming that the 2 m/s² is already present due to an unseen force, allowing for further calculations to determine the necessary horizontal force. The conversation highlights the need for clarity in physics problems to avoid misunderstandings.
p671
Messages
2
Reaction score
0

Homework Statement



slide.png

Homework Equations



F = ma; f = µN

The Attempt at a Solution


Let F' be the action-reaction force between box m and box M
f be the friction on small box m
For small box m:
F' = ma
f - mg = 0
µF' - mg = 0 since f = µF'
µma - mg = 0 since F' = ma
a = g / µ = 9.81 m/s2 / 0.2 = 49.05 m/s2
which is not equal to the given acceleration of 2.0 m/s2
Please help. Thanks



[/B]
 
Physics news on Phys.org
Hello p, welcome to PF :smile:

This is a most peculiar exercise. What you calculate is correct: an acceleration of no less than 5g is required to make m stick to M with so much friction that it doesn't slide down. I find the exercise wording/picture combination very unsatisfactory: It isn't clear at all where the given 2 m/s2 comes from, and -- as you so justly put it -- 2 m/s2 is not 5g at all.

If an answer is absolutely required to get to the next level or something like that, then perhaps it's allowed to make some assumptions: for example that the 2 m/s2 is already there (some jet engine inside M that we can't see) and that the horizontal component of F is supposed to provide the remaining a' = 47.05 m/s2 to the ensemble of (m + M) . You apply Fx = (m+M) a' and some trigonometry to go from Fx to |F|.

Good luck, and maybe you can let us know what came out ?
 
Alright. Thanks! :)
 
Thread 'Voltmeter readings for this circuit with switches'
TL;DR Summary: I would like to know the voltmeter readings on the two resistors separately in the picture in the following cases , When one of the keys is closed When both of them are opened (Knowing that the battery has negligible internal resistance) My thoughts for the first case , one of them must be 12 volt while the other is 0 The second case we'll I think both voltmeter readings should be 12 volt since they are both parallel to the battery and they involve the key within what the...
Thread 'Correct statement about a reservoir with an outlet pipe'
The answer to this question is statements (ii) and (iv) are correct. (i) This is FALSE because the speed of water in the tap is greater than speed at the water surface (ii) I don't even understand this statement. What does the "seal" part have to do with water flowing out? Won't the water still flow out through the tap until the tank is empty whether the reservoir is sealed or not? (iii) In my opinion, this statement would be correct. Increasing the gravitational potential energy of the...
Back
Top