Two painters are working on a platform hanging off the side of a building. The p
ID: 2041190 • Letter: T
Question
Two painters are working on a platform hanging off the side of a building. The platform is 10 meters
long and supported by two cables. The painters are represented by vector forces in the free-body drawing
below. The weights of the objects are: Platform 184 N, Sue 130 N, Jack 220 N. Calculate the force in each
cable when the painters are in the position shown below(Case 1).
To start, locate the pivot point where Cable 1 attached to the platform. Next add the torques produced by each
force about the pivot point together and set equal to zero (?? =0 or better ? F·r?=0 ). Remember that
clockwise (CW) torques are negative Hold your finger on the pivot point so that your paper can rotate but not
slide. Then use you other hand to move the force in the direction of its arrow. If your paper rotates CW the
torque should have a negative sign If it rotates CCW use a plus sign. Not
As Case 2, find out how far Sue can walk towards Jack before there is trouble (platform starts to tip).
Also calculate the force in the cables at this critical point. Hint – When Cable 2 is loose, the force in it is zero.
In solving Case 2, make a free body diagrams (FBD) showing the external forces and the direction of a
positive torque and the pivot point you selected use same pivot point as in Case 1. Show you equation work in
an orderly fashion and enter your results on the bottom of this sheet. Your lab grade will depend on the
accuracy of your work and the clarity of your solution.
After your group has completed the calculations you will test a model to determine if your numbers are
correct. You will turn this lab in before you check your solution on the scale modele that in calculating torques both the
force and distance are always positive. The +/- in front of each torque comes from the direction of impending
rotation.
Distances:
Total platfor is 10 m,
Jack is on the far left, 2.5m to the right of him is cable 1. Sue is 4.0 m to the right of cable one and to the left of cable 2 (the distance between cable 1 and cable 2 is 5.0 m), Cable 2 is 2.5 m away from the far right.
Case 1
CALCULATED
MEASURED
Cable 1
________
________
Cable 2
________
________
Case 2
Cable 1
________
________
Cable 2
________
________
Sue’s Position
(Measure from
left end of
platform)
________
________
LAB 8 Statics & Torque --Equilibrium Two painters are working on a platform cable when the painters are in the position shown below force about the pivot point together and set equal to zer LAB Name HThe Painter's Problem' below. suppotng on a platform hanging off the side of a building. The platform is 10 meters e objects are: Platform 184 N, Sue 130 N, Jack 220 N. Calculate the force in each weights of tThe painters are represented by vector forces in the free-body drawing (Case 1). r point where Cable 1 attached to the platform. Next add the torques produced by each are negative Hold your finger on the pivot point so that your paper can rotate but not v a negative sign If it rotates CCW use a plus sign. Note that in calculating torques both the o ( ??-0 or better ? FTL-0 ). Remember that clockwise (CW) torques slide. Then you other hand to move the force in the direction of its arrow. If your paper rotates CW the force and distance are always positiv rotation. e. The +/- in front of each torque comes from the direction of impending Cable1 able2 2.5m ? 5.0m-2.5m- ack 4.om 5.0m- ?Platform weight walk towards Jack before there is trouble (platform starts to tip). Also calculate the force in the cables at this critical point. Hint- When Cable 2 is loose, the force in it is zero. In solving Case 2, make a free body diagrams (FBD) showing the external forces and the direction of a . Show you equation work in positive torque and the pivot point you selected use same pivot point as in Case 1 an orderly fashion and enter your results on the bottom of this sheet. Your lab grade will depend on the accuracy of your work and the clarity of your solutiorn. correct. You will turn this lab in before you check your solution on the scale model. Case 1 After your group has completed the calculations you will test a model to determine if your numbers are CALCULATED MEASURED Cable 1 Cable 2 Case 2 Cable 1 Cable 2 Sue's Position (Measure from left end of platform)Explanation / Answer
Given:
Platform weight P = 184 N
Sue weight S = 130 N
jack weight J = 220 N
To solve such type of problem take a moment of any one point (where the cable is attached) , i just select the left side of the cable (1), assuming CW direction is positive
- 220 x 2.5 + 184 x 2.5 + 130 x 4 = T2 x 5
T2 = 86 N
we also know that sum all the vertical forcs should be zero.
T1 + T2 = 184 +220 + 130
T1 = 448 N
Case 2:
Basically, trouble will start when T2 = 0, so we have to find the value of distance x.
- (2.5)(220) + (184)(2.5) + (130)(4.0 - x) - 550 + 460 + 520 - 130x = 0
x = 3.31m
At this point, T1 = 448 + 86 = 534N and T2 should be zero.
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