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Questions tagged [homework-and-exercises]

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.

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Calculating RPM of a motor

I am trying to calculate the optimal RPM of a DC motor in order to move a car. I know that the force exerted on the wheel by the motor is: $$F=9N$$ I also know the following information ("h" ...
39 views

Who will win the race?

There is a wedge which is inclined at an angle X to the horizontal.Supppose two carts of same mass M one having 3 wheels and the other having 4 wheels are released from rest at the top of the incline,...
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Frame of Reference in Kinematics

If we have two frames of reference, say S1 and S2, and the acceleration of a particle as seen from both the frames has equal magnitude, say 4 m/s^2, then shouldn't the frames have no relative ...
601 views

Tension in horizontal circular motion of a non-uniform object (friction negligible)

A rod of total mass $M$ and length $x$ has its tip attached to a string of negligible mass, so it spins in a circular motion horizontally free from friction with constant tangential velocity. I have ...
261 views

Variation of a field action

The field action in flat spacetime is $$S = \int d^4x\, \mathcal{L}(\phi,\partial_\mu\phi).\tag{1}$$ The variation in $S$ leads to $$\delta S = \int d^4x\, \delta \mathcal{L}. \tag{2}$$ ...
148 views

Isotropy subgroup of a non-zero vector in 3D space

Recentely i got an assignment for a course of group theory applied to physics, in which i had to find the isotropy group of a vector $v=(1,0,0)^T$ under the euclidean group $E=\mathbb{R^3}\ltimes O(3)$...
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Physics for resistors in parallel which resisto is the warmest [on hold]

for all resistors in parallel, which of the three became warmest when a voltage is applied? Explain your reasoning. Rhigh 9930 ohms, Rm 501 ohms, and Rlow is 17 ohms
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Finding two masses as one rotates about an axis, no givens

My Physics C class was given a lab today with little explanation, and many of us are having issues determining a solution. We are given this apparatus: We must find the masses of both objects m and ...
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Temperature change of water and the copper can

The question is: "0.38kg of a liquid at 12 degrees C is heated in a copper can weighing 0.9kg by an electrical heater of power 20W for 3 minutes. It reaches a temperature of 17C. Assuming no heat loss ...
62 views

How do i calculate the speed of the ball? [on hold]

A spring pushes a 15 grams ball with 10 m/s in a bent pipe. What is the formula to calculate the speed of the ball in point A and point B. The pipe is horizontal so there is no g-force and the pipe ...
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A doubt and different approach regarding “A hypothetical magnetic field existing…”

A popular question from the book HC Verma's Concepts of Physics goes like this:- "A hypothetical magnetic field existing in a region is given by $$\vec{B}=B_{0} \vec{e}_{r}$$ where er denotes the ...
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Question is in description [on hold]

If a volleyball gets served at a height of 2ft at 15m/s from one side of a 60ft court over a 7ft net, what angles will make the ball travel the whole court exactly?
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How to find acceleration with angles included? [on hold]

[![enter preformatted text here]]How do I find acceleration of an object if I have force, mass, friction, and there is 2 given angles (object and force)? I ...
I was reading Polchinski book and there he tries to make a gauge choice to fix the redundacies in the Polyakov action. In order to make this choice, he fixes $$\tau=X^{+}\tag{1.3.8a}$$ and then he ...