Heavy reward, a physics problem, important ideas, process steps!

1) By pulling the object with a force f parallel to the inclined plane, it can be made to slide upwards at a uniform speed, and the resistance in the process of sliding up can be known to be f

So when 3f is pulled, the net force is 2f along the inclined plane

Acceleration can be found using kinematics, and the initial velocity and displacement are known, which can be obtained using 2ax=v 2 ) 0.

The kinetic energy theorem can also be used.

2) In the second question, the idea is to first act on 3f (equivalent to the resultant force of 2f) for a period of time, and then withdraw, which is equivalent to the drag effect of f, and the velocity is exactly zero when it reaches the top.

This question mainly tests the kinetic energy theorem and momentum theorem.

1 Question: Originally, the force of f used the object to move at a uniform speed, that is, the net force was 0, and now the force of 3f is used, that is, there is 2f used to change its speed, here it can be solved by Newton's second law, but it is more troublesome. But with the kinetic energy theorem it is simple, the length of the inclined plane is known, and the work that can be done with the resultant force is equal to the change in kinetic energy, and the initial velocity is 0, so it is simple.

Q2: On the basis of the first question, knowing that the initial velocity is 0 and the final velocity is calculated, we can use the momentum theorem, and the impulse of the resultant force is equal to the change in momentum.

I can't afford to solve the specific problem, think about it yourself, and if you don't understand, look for me. Learn and progress!

1.It is known that f=mgsina [a is the angle between the inclined plane and the ground] So when the force is 3f, the acceleration a=2mgsina can find the velocity from v2=2al The second question will do, but it is not easy to say on the Internet, some things will not be typed.

All correct.

Little red is obtained from p=ui and u=ri p=u 2 r, it is obvious that the rated voltage of the above two bulbs is the same, so u is certain, p is inversely proportional to r.

In the book, p=i 2*r is obtained by p=ui and u=ri, that is, when the current is the same, p is proportional to r.

So it's all correct.

Original].

Both are correct. The textbook says that "the power when electrical energy is converted into heat is directly proportional to the resistance of the conductor" is when the current is constant.

The conclusion of this question is drawn when the voltage is constant.

The power is calculated by p=iu, and according to Ohm's law, two formulas can be derived: p=i2r and p=u2r.

For p=i 2r, we often say that the power is proportional to the resistance, provided that the current is constant.

For p=U2 R, we also say that the power is inversely proportional to the resistance, provided that the voltage is constant.

Therefore, we must not forget the conditions when applying the last two formulas, otherwise there will be an error.

In the title, the 60W electric furnace refers to the power of 60W under the condition of rated voltage, and the electric furnace of 100W refers to the power of 100W under the condition of rated voltage, so it should be calculated by the formula P=U2 R in the case of a certain voltage, that is, the power is inversely proportional to the resistance under a certain voltage.

1. If the spiral on the lampholder is sleeved on the live wire, when the switch is closed, the bulb is broken, and when the bulb is replaced, a single-wire electric shock will occur if the hand accidentally touches the spiral, so that the current in the human body passes through and an electric shock occurs.

2. See figure.

1.For safety, it is difficult for hands to touch the live wire during repairs, and electric shock accidents are not easy to occur.

2.The switch is connected to the live wire, and then connected to the A end of the bulb, and the zero line is directly connected to the B end.

1.Solution: Let the mass containing gold be m1 and the mass containing silver be m2, and the equation m1 + m2 = 280g ...... is obtained1m1 p gold +

M2P silver = 20 cm

2 Simplification of 2, 1, then m1 = then the mass fraction containing gold = Answer: The mass fraction of gold in this handicraft is.

Raindrops fall by two forces: gravity, which is directed downward; Air resistance, direction upward.

When the raindrop reaches the steady-state velocity, the acceleration is 0, the two forces are balanced, m is used to represent the mass of the raindrop, there is mg-krv=0, and v= is obtained

Choosing a is known to refract Sini = sinr, because L = H, all angles of incidence are 45 degrees, then sinr = 1, the refractive index of water is greater than 1, all refractive angles i are less than 45 degrees, according to the cosine theorem of triangles, the answer is a

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