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Results tagged with homework-and-exercises
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user 62726
Applies to questions of primarily educational value - not only questions that arise from actual homework assignments, but any question where it is preferable to guide the asker to the answer rather than giving it away outright. Please READ THE GUIDANCE IN META before asking homework-like questions.
0
votes
Accepted
What is the equation of motion for a driven spring?
Let's check your answer starting back at Newton's 2nd Law:
$$F_{net} = m \ddot{x}$$
$$F_{spring} + F_{gravity} = m \ddot{x}$$
$$-k (x - x_{spring} - l) + m g = m \ddot{x}$$
$$-k (x - a sin(\omega t) …
- 7,595
1
vote
mechanics problem: rope on a fictionless table through a hole
I think the author has forgotten to mention that the part of the rope on the table is stretched out in a straight line, otherwise, I would say the way it's piled does make a difference, and the proble …
- 7,595
2
votes
Direction of velocity confusion on inclined plane
Let's look at the two options:
Taylor's expression:
$$\dot{q_1} cos(\alpha)+\dot{q_2}$$
Your expression:
$$\dot{q_1} cos(\alpha)-\dot{q_2}$$
Since the wedge will be moving to the left, $\dot{q_2}$ …
- 7,595
3
votes
Accepted
Determining a temperature increase from heat energy
Q is the heat gained by the water. In this problem, the thermal energy gained by the water must come from the kinetic energy the bullet lost in the water.
Find the kinetic energy lost by the bullet, …
- 7,595
2
votes
Accepted
How do I find the angle with respect to the ground that will cause a projectile launched fro...
Note that a constant horizontal acceleration is not a realistic model for the force due to a breeze, but putting that aside: the basic kinematics equations for 2D motion of an object undergoing accele …
- 7,595
0
votes
The storage of kinetic energy in a flywhell?
The kinetic energy of a flywheel is given by
$$T = \frac{1}{2} I \omega^2$$
Where $I$ is the moment of inertia and $\omega$ is the angular speed. The specific kinetic energy (KE per kilogram) is
…
- 7,595
1
vote
Would a non-conducting body ever acquire a uniform static charge throughout it's volume?
An electret is a insulating material that has been imbued with a semipermanent volume charge distribution by bombarding it with charged particles. I don't know how uniform the charge distribution gen …
- 7,595
12
votes
Accepted
Electric Field of Hollow Cylinder
I'm assuming here that the cylinder is "infinitely long", or at least very long so that $h >> r$. Otherwise, there are complicated non-integrable "end effects", but it doesn't look like you're intere …
- 7,595
2
votes
Accepted
The equivalent resistance betweeen A and B. I need the answer with proper explaination
You have two basic options:
Realize that this is actually just two resistors in series with three parallel resistors, and analyze it using the equivalent resistances of resistors in parallel and ser …
- 7,595
3
votes
Accepted
Tangential velocity of a parabola
If you want the vector velocity, it's straightforward to use kinematics - if you know the velocity at the beginning, the horizontal component is constant throughout the parabola,
$$v_x(t) = v_x^0$$
…
- 7,595
0
votes
Accepted
Rate of deceleration for an average speed
You're almost all the way there. You figured out that the "average speed" info gives you the time ($4.17s$) it takes for the car to cover $25m$.
Now all you have to do is find the acceleration.
You …
- 7,595
0
votes
Theoretical uncertainty of a circuit's total resistance when made entirely of resistors
Let's say we have a bunch of resistors. Let's call the "ith" resistor $R_i$ with fractional tolerance $t_i$. In that case, each resistor's actual value is somewhere in
$$R_i \pm R_i t_i$$
If we conn …
- 7,595
4
votes
Geodesic equation proof confusing me
The step between (4) and (5) is an application of the chain rule. If you follow each of the terms carefully, you can see that
$$u^t = \frac{dt}{d\tau}$$
I think one of the reasons it's confusing is t …
- 7,595
3
votes
Accepted
What happens with an originial force if a part of it creates a torque?
The force doesn't get "used up" by creating a torque. The torque and the force exist simultaneously.
You correctly computed the torque due to that force. If that is the only force on this object, t …
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0
votes
What should the length of my wire be in order to get a surface area of 10cm^2?
The key idea here is that the volume of the wire before and after flattening it should be almost exactly the same, since you aren't removing or adding any metal, just smushing it around.
If $L$ is th …
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