A little confused about physics, a physics puzzle

Physics is a process of understanding, and the process of listening and writing questions is a process of understanding. You can make this same type of problem together, and in the process of doing it, you will feel that you are getting better and better, and there are things that you don't understand very well, so it is very useful to read more notes and do some simple basic experience.

I have been fond of physics since I was a child, and I usually pay attention to observing some physical phenomena in life, such as hitting up and down when the lid of the kettle is opened. When braking on the road, there will be black brake marks and some smell similar to burning rubber, I will ask myself how these phenomena come about, combined with the physics knowledge I learned in class to ask and answer myself, so that I can get a high score in the physics exam without reviewing.

The key in these years depends on communication with teachers.

I guess you might as well be here to ask for your help.

Have a good talk with the physics teacher for half an hour.

Hehe. That's how my physics grades came up.

This kind of problem, light rope and thin rope, no air resistance, if the object does not move, there is no energy loss. So the angle between object B at its highest point and in the vertical direction is equal to 60. If object A moves, it is different, due to the rough slope and friction, it will lead to energy loss, and the highest point of each vibration will be reduced until object A no longer moves, and the vibration will be stabilized, but this topic does not exist in the motion of object A, friction does not do work, and the mechanical energy of the system is conserved, so the highest is 60, and it will return to the position where object B is released after a cycle of vibration.

Since I can't see the diagram, I will provide an idea, that is, the pull force of object B on the rope at the highest point and the lowest point will be different, and the pull force on object A will be different, and the title mentions that it happens not to slide, that is, among the two tension forces, object A does not slide down when it is the smallest, and when the pull force is the largest, object A happens not to slide upward, which just means that it is the maximum static friction. Then the maximum static friction can be obtained, and f is half of the difference between these two tensile forces. Then, according to the fact that object A has no motion and the force is balanced, the sliding force of the gravity of object A can be calculated, f=f large tensile force - f = f small tensile force + f.

With f it is possible to calculate the mass of object A, f=mgsin30.

If there is a loss of energy.

Where to go???

"A physical puzzle This beaker is placed on the scale, and the table tennis ball and rope are installed (the quality of the table tennis ball is relatively different from the water), the table tennis ball will be subject to buoyancy, and the buoyancy will give the whole a lifting force, and this lifting force is just offset by the water discharged, so the value of the scale should be reduced? "

Is the buoyancy acting on the ball, and the ball is connected by a rope beaker, so the upward buoyancy is transmitted to the beaker, and the beaker is subjected to the upward tension scale, which should be reduced but not not? Newton's theorem is a loophole, right?

No! It is precisely because of the incomplete understanding of Newtonian mechanics that Newton said that the action of force is reciprocal. Who gives the buoyancy to the ball?

It's water. Since the action and reaction occur at the same time, the pellet also gives a reaction to the water, and this reaction is also transmitted by the water to the beaker. The buoyancy of the ball is transmitted to the beaker by the rope, and the reaction of the water is also transmitted to the beaker by the water, and the two effects are roughly equal and the direction is opposite, so the weight of the beaker does not change, and the scale does not change.

First, this is not Newton's law. Second, buoyancy only acts on table tennis balls, and has no effect on the whole No matter how you use the rope. Buoyancy does not change the number of scales.

I saw a cartoon the other day. A man wears a steel helmet on his head and holds a pole with a magnet on it. This man opened and flew into the sky by magnetic force.

Let element A be x and B be y, then there is x:y=a:b, y:12=c:d, so solving the equation gives x=(a b)*(c d)*12

First of all, the car and the sand are observed as a whole, because the force between the two is an internal force (the combined external force is zero), so the momentum of the system is conserved.

Initial state: The car and the sand have the same velocity, let the total momentum at this time be p.

Intermediate physical process: The moment the sand leaves the car, the sand also has a velocity due to inertia, and the speed at the time of the hole is the same as the speed before leaving the car (i.e., the speed of the sand before and after leaving the car is unchanged).

The final state: the mass of the sand and the car remains unchanged, the speed of the sand in the initial state and the final state is also unchanged, and the root difference is conserved according to the momentum, will the speed of the car change?

1. If the object is still stationary on the ground, then its net force is 0n, and when there is no other vertical force, it is still supported by the ground facing it. If you think about it, if you don't give it such a vertical upward pull, won't it still move? Rest is also a state of equilibrium, and the net force in the equilibrium state is 0.

2. The kite is originally balanced, and the resultant force is 0 when balanced, that is to say, the resultant force of the kite is the same as the rope tension except for the rope tension, and the direction is opposite. The rope broke suddenly, and the kite remained in its original state due to inertia, so the wind force was still unchanged for a moment, so the combined force of wind and gravity remained unchanged instantly.

1 Because the tensile force of 20N is smaller than the heavy force of 50N.

So we know that the object is still at rest on the ground, because of the existence of the supporting force, the object can be at rest, and the net force of the object at rest is 0

2 The kite is balanced by the combined force of gravity, the wind and the pull of the rope, that is, the net force is 0, according to the nature of the action and reaction force, that is, Newton's third law, we know that the resultant force of gravity and wind is equal to the pull force of the rope on the kite and opposite in the direction.

1 30n

Because "under the action of a vertical upward tensile force of magnitude 20n", then 50-20 = 302

The direction is on the extension along the rope, and the resultant force is 2n

Because "the wind and the pull of the rope work together to maintain balance".

is in equilibrium and the resultant force is 0

After it is broken, there is no force to balance the resultant force of gravity and wind, so it can be seen that the combined force of gravity and wind is the pulling force of the rope to the kite.