Tagged Questions
1
vote
1answer
41 views
How large of a solar sail would be needed to travel to mars in under a year?
I'm attempting to approach this using the identity
$$F/A = I/c$$
I can solve for Area easily enough
$$A = F(c/I)$$
and I know the distance $d$ is
$$d=1/2(at^2)$$
But I'm having difficulty trying to ...
2
votes
2answers
63 views
Hamiltonian of Harmonic Oscillator with Spin Term
We have the usual Hamiltonian for the 1D Harmonic Oscillator:
$\hat{H_{0}}=\frac{\hat{P^2}}{2m} + \frac{1}{2}m \omega \hat{X^2}$
Now a new term has been added to the Hamiltonian, $\hat{H} = ...
-1
votes
1answer
25 views
Terminal velocity and force pull [closed]
I can't figure out this problem .
Buoyancy force and gravity remain constant and viscous force by is $-kv$. And these forces all balance, but data isn't given according to that, or I am not able to ...
1
vote
1answer
35 views
Finding the coffecient of restitution
A ball moving with velocity $1 \hat i \ ms^{-1}$ and collides with a friction less wall, afetr collision the velocity of ball becomes $1/2 \hat j \ ms^{-1}$. Find the coefficient of restitution ...
-1
votes
1answer
86 views
Confusions about rotational dynamics and centripetal force
I am a high school student. I am having confusions about the centripetal force and rotational motion . I have known that a body will be in rest or in uniform velocity if any force is not applied. But ...
0
votes
1answer
59 views
A sphere rolling down a rough wedge which lying on a smooth surface
A sphere of mass $m$ and radius $r$ rolls down from rest on an inclined (making an angle $\phi$ with the horizontal ) and rough surface of a wedge of mass $M$ which stays on a smooth horizontal floor. ...
2
votes
1answer
135 views
Mechanics question
The following is a question from a past exam paper that I'm working on, as I have an exam coming soon. I would appreciate any help.
A fairground ride takes the form of a hollow, cylinder of radius ...
3
votes
3answers
62 views
Friction on roads
I have a question with which I am having trouble.
A 71m radius curve is banked for a design speed of 91km/h. Given a coefficient of static friction of 0.32, what is the range of speeds in which a car ...
0
votes
1answer
82 views
Shear Flow corresponding to Eccentric Shear Force of a Closed-section Beam (Structural Analysis - Mechanics)
Been stumped with this question for way too long... its a beam with a thin-walled rectangular cross-section, and a shear force is acting at a distance from the shear center. I know my decomposition of ...
0
votes
2answers
101 views
How do you tell what forces do no work?
The total mass of the children and the toboggan is 66 kg. The force the parent exerts is 58 N (18 degrees above the horizontal). What 3 forces/ components do no work on the toboggan?
I said the ...
0
votes
0answers
118 views
Maximum Shear on a Beam - beam with fixed support on one end and hinge on other end
A beam $\displaystyle 3m$ long with fixed support on one end and hinge on the other end is subjected to a uniform load of $10\ kN/m$. What is the maximum shear of this beam?
The solution is this one:
...
2
votes
2answers
145 views
Cantilever Beam - Maximum Shear of the Beam
A cantilever beam $3\ \text{m}$ long is subjected to a moment of $10\ \text{kNm}$ at the free end. Find the maximum shear of the beam.
The answer is "There is no vertical load, shear is zero"
...
4
votes
1answer
79 views
Finding the acceleration of a cart rolling on a table
The cart is rolls frictionless on the table. It has a mass of $1 kg$. Attached to it are 2 strings, that go through two frictionless sheaves. The weights have masses as in the picture.
...
2
votes
4answers
203 views
Pseudo force in rotating frames
A bug of mass $m$ crawls out along a radial scratch of a phonographic disc rotating at $\omega$ angular velocity. It travels with constant velocity $v$ with respect to the disc.
What are the forces ...
2
votes
0answers
89 views
Internal moment in the hull of a pressure vessel
This question is related to the course structural analysis. As part of our exam grade every student has been given different multiple homework assignments which we have to solve.
One of the problems ...
1
vote
0answers
78 views
What is the angle of the string with the vertical?
A heavy uniform sphere of radius $a$ has a light inextensible string
attached to a point on its surface. The other end of the string is
fixed to a point on a rough vertical wall. The sphere ...
0
votes
0answers
143 views
Change in time period of pendulum [closed]
A pendulum of effective length $L$ has a bob of radius $R$ filled with water. If the water freezes to ice, what is the change in the time period of the pendulum?
0
votes
0answers
74 views
How do I figure out the normal force on a person on an accelerating platform? [closed]
My question is an elaboration on this question: Force on rope with accelerating mass on pulley
The elaboration is to determine what the Force that the platform exerts on the person. Assume the ...
0
votes
0answers
25 views
Determine the dilation temperature so as to double the speed
There's a metallic rod of length $l_1$ which is spinning around a vertical ax which passes through its center. The ends of the rod are spinning with $\omega_1$ angular speed. Determine the temperature ...
1
vote
3answers
425 views
Is it possible to find out the distance traveled by a car if the force applied on it is given?
Say you have car which produces $F$ amount of force which is transferred to the wheels directly.
Now assuming that there is air friction which is causing a retarding force proportional to the ...
1
vote
2answers
70 views
Mechanics Energy (Calculus)
A particle moves with force
$$F(x) = -kx +\frac{kx^3}{A^2}$$
Where k and A are positive constants.
if $KE_o$ at x = 0 is $T_0$ what is the total energy of the system?
$$ \Delta\ KE(x) + \Delta\ ...
0
votes
1answer
105 views
Why is my speed imaginary?
A particle is released from a dense atmosphere free planet of radius r at a distance R (R >> r ). find the speed on impact.
$$F = \frac{GmM}{(r + R)^2} = m \frac{dv}{dt} = mv\frac{dv}{dR}$$
...
0
votes
0answers
57 views
Helium Balloon Reaction [closed]
Suppose we have Bob the astronaut sitting without a space suit in a spaceship full of air on a mission to Mars. Bob is very fond of balloons and is holding on to a nice, big, red helium balloon via a ...
0
votes
1answer
155 views
two pendulums, which pendulum has shorter period [duplicate]
Possible Duplicate:
A pendulum clock problem
There are two pendulums.
First pendulum consists of a rod of length L and flat heavy disk of radius R (R < L), disk is connected rigidly to ...
1
vote
1answer
209 views
How to find the value of the parameter a in this transfer function? [duplicate]
Possible Duplicate:
How to find the value of the parameter $a$ in this transfer function?
I am given a transfer function of a second-order system as:
$$G(s)=\frac{a}{s^{2}+4s+a}$$
and I ...
1
vote
1answer
83 views
How to find the value of the parameter $a$ in this transfer function?
I am given a transfer function of a second-order system as:
$$G(s)=\frac{a}{s^{2}+4s+a}$$
and I need to find the value of the parameter $a$ that will make the damping coefficient $\zeta=.7$. I am not ...
2
votes
3answers
565 views
Example in the book: A simple accelerometer
A simple accelerometer
You tape one end of a piece of string to the ceiling light of your car and hang a key with mass m to the other end (Figure 5.7). A protractor taped to the light allows you ...
2
votes
1answer
625 views
Confused with stress, strain and linear thermal expansion
Four rods A, B, C, D of same length and material but of different
radii r, 2r , 3r and 4r respectively are held between two rigid
walls. The temperature of all rods is increased by same ...
1
vote
2answers
74 views
Acceleration: Value Disparity?
If we consider a ball moving at an acceleration of $5ms^{-2}$, over a time of 4 seconds, the distance covered by the ball in the first second is $5m$. In the 2nd second will $5 + 5 = 10m$. In the ...
1
vote
0answers
163 views
Exam review question on thermodynamics [closed]
A cube has a side length of $20\text{ cm}$.
An atom in the gas moves around the cube as shown.
It continually bounces off the four lateral walls of the cube.
The atom has a mass of $6.6\times ...
0
votes
0answers
105 views
Dynamo-meter and forces problem [closed]
I have this system:
Where D stands for dynamo-meter, and you can exclude all lines\dynamo-meters\balls weight and friction.
The left ball connects to body A, and the right ball connets to the wall.
...
0
votes
2answers
1k views
Work done by spring over distance
I'm working through a problem involving energy conservation. Unfortunately, I cannot calculate the work done by a spring.
...
2
votes
1answer
416 views
Force on rope with accelerating mass on pulley
I have a pretty basic pulley problem where I lack the right start.
A child sits on a seat which is held by a rope going to a cable roll (attached to a tree) and back into the kid's hands.
When it ...
0
votes
1answer
71 views
How must you spin the ball to make it alternate between 2 positions? [closed]
Assume any parameters you may need. Thanks in advance.
0
votes
3answers
550 views
Impulse - distance question
What impulse should be applied to an object of mass m, having a known coefficient of friction u to get to a distance d ?
Thanks!
Update 14.02.2011:
I still wasn't able to find an answer to this. ...
0
votes
2answers
2k views
Homework Help - Physics / Calculus III / Force-Work Problem
I have tried to answer the problem correctly, and I have found similar (and even an identical) problem in my textbook, yet I still can't seem to yield the correct answer with this specific problem.
...
0
votes
2answers
559 views
Mechanical energy problem
Question goes: "An anvil hanging vertically from a long rope in a barn is pulled to the side and raised like a pendulum 1.6 m above its equilibrium position. It then swings to its lowermost point ...
0
votes
3answers
672 views
4th equation of motion
Ive been given the 4 equations of motions The fourth being:
$$s=ut+\frac{1}{2}at^2$$
If rearranged it forms the quadratic equation
$$at^2+2ut-2s=0$$
But that means that t has 2 values.
Will ...
0
votes
3answers
3k views
Period of Precession
I'm trying to find the period of precession for a gyroscope. Now I was able to find the angular precession rate, which was 1.132 rad/s, but I have no idea how to convert this to a 'period', and google ...
1
vote
2answers
266 views
Angular Momentum and Force
I'm stuck on number 5. The answers to the first 4 are correct, but I dont know how to set up number 5. Any idea that I would have would require me having some kind of time information, but thats not ...
1
vote
2answers
1k views
Angular Momentum and Average Torque
Refer to number 6. This is the one I'm stuck on. So angular momentum is conserved right, so initial angular momentum is equal to final angular momentum. Initial is 7.87 so final must be 7.87, right? ...
1
vote
1answer
683 views
Finding angular acceleration from torque
We have to analyze this video
Givens:
An applied net torque due to the wind on the windmill is equal to 1500 N*m.
Each (of the 3) propeller props weighs approximately 45 Kg and has a Moment of ...
