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4

Okay, this seems to me correct since the force imparted by $q'$ on $\left(Q- q'\right)$ is cancelled by the field of $q$ since it is a zero equipotential surface of $q-q'$ system. I have no idea why you think a zero potential surface has anything to so with anything. While the field of $q$ and the field of $q'$ together make a zero potential surface on ...

2

It's a general consequence of Newton's Laws of Motion that an object is stationary when no net forces or momenta act on it. Avoiding net forces or momenta is precisely what makes perfectly balancing a rectangular block on a triangular one so difficult. Above is a rectangular block with mass $m$, perfectly balanced on a triangular block. I've added the ...

1

The point is that the ball gets a tangential hit by the ground. This changes the angular momentum of the ball. Consider a ball thrown with a horizontal speed v. It should also not rotate. Right before hitting the ground, the ball has an angular momentum of $$L=mvr$$ This is a result of $\vec{L}=\vec{v}\times\vec{p}$, which is also valid for linear ...

1

The simple word is "damping". Initially when you hang an object from a string (spring, etc), it will move - side to side, and up and down. While it is moving, there will be a changing force on the object - after all it is accelerating / decelerating. This shows up as a force in the string that changes with time. In all "real" systems, there is also a ...

1

When the light hangs off the ceiling by means of the electrical cable, the cable actually acts as a very stiff spring. The light bulb provides a downward force due to its weight $mg$. The cable acts like a spring, slightly idealised here as a Hookean spring which provides the counter force (what you called the force of tension) of $k\Delta y$ with $k$ the ...

1

As @rmhleo pointed out in his answer, the frictional force doesn't depend on the surface area, because no matter which part of the object is in contact with the other surface, the total normal force (and thus the total frictional force) is unchanged. However, that assumes a couple of simplifying conditions: namely, that the two surfaces are consistent in ...

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