- #1
TomK
- 69
- 14
- Homework Statement
- Q18 (Section 2), ENGAA 2019
- Relevant Equations
- Moment equation.
The correct answer is 'B'.
I would like some clarification, in regard to the forces that exist in this moments problem.
General Queries:
1) Is there friction acting on the hinge in a downward direction (parallel to the wall)? Does the ramp being "smoothly hinged" to the wall mean there is no friction acting on the hinge?
If friction did exist, would there be a reaction force (since: friction = mu x reaction), acting perpendicular to the wall, from where the hinge is in-contact? Would the direction of said-reaction force change, depending on how the ramp is angled?
2) It is stated that the string is "light" (of negligible mass) and "inextensible"? If the string could extend, how would that affect the way you solve the problem? Wouldn't you just find the moments as normal? Would you have to do energy calculations, due to elastic potential energy in the string?
3) Where the string is fixed to the wall (at the top), does a reaction force exist, acting perpendicular to the wall, from where the string is in-contact?
4) Why does it matter that the ramp is lowered "at constant speed"? Would it affect the tension in the string?
Worked Solution Queries:
I looked at this worked solution (http://www.engineeringadmissionsassessment.com/2019-solutions.html) - scroll-down to the bottom of the page to see working for Q18, Section 2.
It looks like they start solving the problem when the ramp is fully-horizontal, when the angle between the wall and ramp is 90 degrees.
How can they say that the angle between the string and ramp is 'theta/2'? Doesn't this assume it's an isosceles triangle, where the 'distance between the winch and hinge' = 'length of ramp'?
I have a lot of confusion over this question and how to start it.
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