Engineering Mechanics - Friction - Discussion

Discussion :: Friction - General Questions (Q.No.1)


The boy at D has a mass of 50 kg, a center of mass at G, and stands on a plank at the position shown. The plank is pin-supported at A and rests on a post at B. Neglecting the weight of the plank and post, determine the magnitude of force P his friend (?) at E must exert in order to pull out the post. Take B = 0.3 and C = 0.8.

[A]. P = 360 N
[B]. P = 264 N
[C]. P = 229 N
[D]. P = 293 N

Answer: Option B


No answer description available for this question.

Aswathvignesh said: (Jun 10, 2011)  
How to solve this problem?

Mani said: (Jun 16, 2011)  
Ya how to solve the problem?

Swapnil Dafal said: (Oct 16, 2011)  
Draw the free body digram (FBD).

Then take sammetion of fx & sammetion of fy equal to zero and find moment with respect to point a. Also apply work energy principle for bettting third equation.

Vignesh said: (Mar 28, 2012)  
Here should we take planck and post as two bodies and draw the free body diagrams for each of them? please explain the procedure!

Rohan said: (Apr 9, 2012)  
Draw fbd of the diagram then calculate summation of x and why separately also take moment at point a.

Nasma Noor N V said: (Mar 26, 2014)  
I am getting two different answers if we take first fbd of plank and then post. If we take moment about the base for post am getting 264N. If I take sum of forces in x and why direction am getting 284. 1.

Alfredo said: (May 25, 2015)  
I need more explanation to your solution thank you and regard.

Lira said: (Jun 1, 2015)  
I still don't understand how do you get into the answer?

Hasan said: (Jun 4, 2015)  
I want the details of solution?

Madara said: (Apr 12, 2016)  
Explain the solving method of this question.

Sumit Manna said: (Jul 23, 2016)  
Force create at A=50g/3 and force in B = 100g/3 verticaly both Friction force is 0.3 * 100g/3 at B.
Moment about C : 0.3 * 100g/3 * (0.3 + 0.4) = Fcos30 * 0.3.

So F= 264N.

James Oketch said: (Feb 13, 2017)  
Not able to reach the answer. Please explain me in detail.

Debolina said: (Aug 26, 2017)  
Please solve it clearly.

Goku said: (Nov 27, 2017)  
Please explain about C @Sumit Manna.

Shree said: (Oct 23, 2018)  
Please explain in detail @Sumit manna.

Ajay Kumar said: (May 13, 2019)  
How? Please explain the answer.

Ajay Kumar said: (May 13, 2019)  
Please solve it.

Chethan said: (Jul 4, 2020)  
Take vertical forces equal to zero, Ay + Ny = 490.5.
Take moment at A, then Ny*3=mg*2, By solving we get N=327.
Friction force = static friction coefficient * normal force.
f = 0.3 * 327 = 98.1;
Now take moment at c(post bottom),we get f(0.3+0.4) = Fcos30 * 0.3
By solving the above equation we get F = 264.115 Newtons.

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