Engineering Mechanics - Friction - Discussion
Discussion Forum : Friction - General Questions (Q.No. 1)
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.
Discussion:
19 comments Page 1 of 2.
Chethan said:
5 years ago
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.
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.
Nasma noor n v said:
1 decade ago
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.
Swapnil dafal said:
1 decade ago
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.
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.
Sumit manna said:
9 years ago
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.
Moment about C : 0.3 * 100g/3 * (0.3 + 0.4) = Fcos30 * 0.3.
So F= 264N.
Vignesh said:
1 decade ago
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:
1 decade ago
Draw fbd of the diagram then calculate summation of x and why separately also take moment at point a.
Alfredo said:
1 decade ago
I need more explanation to your solution thank you and regard.
James Oketch said:
9 years ago
Not able to reach the answer. Please explain me in detail.
Lira said:
1 decade ago
I still don't understand how do you get into the answer?
Madara said:
9 years ago
Explain the solving method of this question.
Post your comments here:
Quick links
Quantitative Aptitude
Verbal (English)
Reasoning
Programming
Interview
Placement Papers