Tagged Questions
2
votes
1answer
58 views
Tension in a closed loop around an object, carrying stuff
Sorry when this sounds like a first year physics homework question, but it's actually not. It arose during a discussion regarding safe practices for rock climbing anchors...
So here we go: Imagine ...
12
votes
5answers
1k views
Why Won't a Tight Cable Ever Be Fully Straight?
I posted this picture of someone on a zipline on Facebook.
One of my friends saw it and asked this question, so he could try to calculate the speed at which someone on the zipline would be going ...
0
votes
1answer
32 views
Find the bending moment of a pole attached to a moving block
I'm having trouble with the following problem.
What I've done so far:
x-y is the usual coordinate system.
$a=\frac{F}{m}=\frac{800}{60}$ and the y component of this is $a_y=a\sin{60^\circ}$.
To ...
1
vote
1answer
140 views
Cylinder rolling down an inclined plane held by a string
A cylinder of mass M and radius R is in static equilibrium as shown in the diagram. The cylinder
rests on an inclined plane making an angle with the horizontal and is held by a horizontal string
...
3
votes
2answers
207 views
Bowling ball on a rubber sheet
After reading a layman's guide to general relativity, I began to wonder what shape a bowling ball on a large rubber sheet would produce. For simplicity, I would like to assume that Hooke's law applies ...
0
votes
3answers
134 views
Doubts with levers
I'm studying for a test of static rigid body and I'm having doubts on how to solve problems involving levers with weight.
If I have, for example, a lever 10 kilograms and 3 meters long and one support ...
4
votes
1answer
742 views
Solving a statically indeterminate truss
I'm trying to solve the statically indeterminate truss shown below and I'm having a little trouble.
$H$, $P$ and $\beta$ are given. The material is aluminum (density is 2700 ${kg/m^3}$) and has a ...
0
votes
1answer
140 views
Relationship between torques and centre of mass or centre of gravity [closed]
1) A wardrobe is $2$m high and $1.6$m wide. When empty, it has a mass of $110$kg and its centre of gravity is $0.8$m above the centre of its base. What is the minimum angle through which it must be ...
1
vote
1answer
60 views
Force in tetrahedron edges
I am looking for a formula that enables me to calculate the force in a tetrahedron edge such that it relates $F_b$ with $F_z$ through the beam thickness and length. I have the following assumptions:
...
0
votes
1answer
276 views
Torque and equilibrium
I am a little stuck on the concept involved in part b) of the following problem:
A $5 m$ long road gate has a mass of $m = 15 kg$. The mass is evenly distributed in the gate. The gate is supported at ...
0
votes
1answer
327 views
Calculating torque in a structure
I posted this on math stack exchange but realize it is more a physics question.
I have a structure which is set up as shown in the image. A weight hangs from point A with mass $m$. Joint B is free ...
2
votes
1answer
279 views
Why does the beam in a weighing balance get tilted proportional to the weights added to each pan?
I'm talking about a beam balance(a simple weighing balance with a beam and two pans hung on either side)
As answered in a previous question, the beam comes back to the original position when one ...
2
votes
2answers
868 views
Angles on swing sets
I'm building a swing set for my children. All of the designs I've seen involve building two A-frames and connecting them at the top with a crossbar/beam from which hang the swings. The A-frames are ...
1
vote
1answer
449 views
Calculating mass of object by lifting edge
Assuming a solid rectangular plate, hinged along one edge. How does one calculate the mass of the plate if the force necessary to lift the opposite edge is known?
0
votes
1answer
208 views
Bridge Trusses?
Which kind of truss would produce the best result (aka. best distribution of force):
i) An equilateral, isosceles or a scalene triangle
ii) 3 small triangles or 2 big triangles (the overall masses of ...
3
votes
3answers
720 views
Deadlifting the rear end of a car with a lever. What it equates to in actual weight?
Consider this youtube video of a guy lifting a car. (skip to 2:15).
I checked, and these cars (PT Cruiser) weigh $1417\:\rm{kg}$. What would the equation be to estimate how much weight he is actually ...
-1
votes
1answer
122 views
Find largest angle
The two homogeneous bars AB and BC are connected with a pin at B and
placed between rough vertical walls. If the coefficient of static friction between
each bar and the wall is 0.4, determine the ...
1
vote
1answer
130 views
Finding the contact force in a mechanical problem [closed]
what is the proper FBD for this system. I cant decide since the weight is given, but there is tension and contact forces. Things get mixed up.
Determine the contact force between the smooth 200-lb ...
0
votes
2answers
1k views
How do I find the tension in additional strings in this problem?
A mass of 5.00 kg hangs attached to three strings as shown in the figure (see image below). Find the tension in each string. Hint: Consider the equilibrium of the point where the strings join.
...
0
votes
1answer
992 views
Moment calculation [closed]
Consider image below. The weight of the fire-fighter is 840 N. What is the torque of the fire-fighter's weight about P and what is the value of the force C which cancels out the torque?
7
votes
2answers
2k views
What is the force on the arms in a pushup?
What force do the arms have to generate to do a pushup? Let us look a this simplified model:
The body can be represented by the green plank of mass B. Its angle to the ground is $\theta$.
This ...
1
vote
4answers
2k views
Upward force on a object at rest
Is there an upward force on a object at rest? If yes, where does it come from?
