A few physics questions in the second year of high school are not difficult, but I can t. Solve

1。The idea of solving this problem is that the impulse is equal to the amount of change in momentum.

The velocity is 4m s before contact and the column is conserved after that.

f-mg）*t=mv

The impulse obtained is 1

2。The problem is that the impulse of the frictional force is equal to the impulse of the tensile force (substance or momentum theorem) 2t* mg-f*t=0

3。The rated power of the car is certain, the friction is unchanged, then there is always a moment when the power can reach the rated power, at this time p = f pull v, f pull - f friction = ma, a certain, the size of the traction force can be known, the speed is naturally known, because the acceleration remains constant.

The time is known by a=vt.

There are still problems.

1. The sum of the impulse of gravity on the ball and the impulse of the cushion on the ball is zero. i(pad) i(weight) 0,i(pad) mg t(fall) direction up.

2. The action time of friction force is 2t, the action time of tensile force is t, and the sum of the impulses of the two forces is 0 (the momentum at the beginning and end is 0). So 2 mgt-ft=0

3. The maximum speed of uniform speed in this question is different from the maximum speed of driving in the first question. Because at the maximum speed of travel, the traction force is equal to the drag. The maximum speed traction force of a uniform variable speed is equal to the sum of the drag force and the resultant force.

So by p fv,f (f resistance f combined)v=at, t=16s can be obtained

As illustrated, how does there exist a "synthesis of forces"?

According to the meaning of the text in the diagram, perhaps the problem situation should be a hanging L-shaped member, one end of the object of mass of M1, the other end of the object of mass of M2, the corresponding member length is L1, L2, when the angle between the two rods and the perpendicular line is balanced, the ratio of M1 and M2 is found. This involves the problem of moment balance, when the member is balanced, there is m1 l1 sin = m2 l2 sin, when the intersection angle of the two rods and the perpendicular line is equal, there is m1 l1 = m2 l2, that is, m1 m2 = l2 l1.

If the angle between the two rods and the perpendicular line is unequal, then m1 m2 = l2 sin 2 l1 sin 1.

Please finish this physics problem before you can leave.

If you don't make your topic clear, it's unsolvable.

For the first question, it is necessary to understand the difference between electric potential and electric potential posture and defeat energy, the electric potential is only related to the source charge, and has nothing to do with the positive or negative of its own charge, so from m to p the electric potential increases, the electric potential trace flutter energy decreases.

In the second problem, the problem is solved if the electric potential at infinity is 0.

The electric potential at infinity and on the Earth's earth is 0.

1.Increased internal energy = absorbed heat energy - water vapor does external work, water vapor is not like liquid water, it can spread around, to overcome gravity and atmospheric pressure, this will lose energy, need more heat energy supplement.

2.e is the work done by friction, the work done by friction w=fs, f is the friction between the bullet and the wooden block (sliding), s is the relative displacement of the bullet to the wooden block when it passes through the wooden block, note: it is relative!

That's the length of the block. F and s are equal in both cases, aren't they? So.

e equal. As for time, think about it, the acceleration of the wooden block is the same in both cases, because the sliding friction is equal. In the two cases, the relative displacement of the bullet from the time it touches the wooden block to the time when it comes out of the wooden block is not the same!

Moreover, the initial velocity of the collision with the wooden block is the same in both cases, and the initial velocity and acceleration are the same, so the greater the relative displacement, the more time there is.

4.There is heat energy generation, that is, the resistance does the work, don't forget that the work done by the resistance on the two objects consumes mechanical energy and becomes internal energy. The second question is the same resistance, if a person hits a wall and does not move, can you say that the momentum decreased by the person is equal to the momentum increased by the wall? Hey.

Question 1: The law of conservation of mechanical energy, when the volume increases, work is done to the outside world; On the contrary, if the volume decreases, the outside world will do work on it. Since the mechanical energy is conserved, the value of its external work plus the increase in internal energy is equal to the energy absorbed, so the increase in its internal energy is less than the energy absorbed.

Question 2: In the case of a bullet passing through a wooden block, the increased internal energy of the wooden block is always equal to the product of the resistance experienced by the bullet when passing through and the relative distance between the two, which in this question is equal to the thickness of the wooden block; If the bullet does not pass through the block, the relative distance is equal to the distance the bullet penetrates in the block. In this problem, since the resistance of the two neutron bombs is equal and the distance is equal to the thickness of the block, the internal energy increased by the block is equal.

Question 3: Since the ball expands and does external work, and because the density of mercury is greater than that of water, then under the same circumstances, the external work done by ball B is greater than that of ball A; And since the temperature is the same, that is, the internal energy of the two balls is the same. Therefore, the heat absorbed by the B ball is greater than that of the A ball.

Question 4: Since the total energy is equal to the mechanical energy plus the internal energy, there is the internal energy that is converted to the wooden block during the process of the bullet passing through the wooden block, so the mechanical energy of the bullet should be greater than the mechanical energy of the wooden block. However, the conservation of momentum has nothing to do with the change of energy, and in high school physics, almost all such problems satisfy the law of conservation of momentum.

1 Let's assume that the water is contained in a container, then the volume will increase when it changes to gas, the gas has pressure on the wall of the container, and it can be seen that the gas does work externally from w=fs 2 From e=fs f is the friction between the bullet and the wooden block, s is the relative displacement, and the change of e is equal, and then the vt diagram of the bullet can be used to compare the time 3 The two balls will do work on the outside world when the volume increases, and the reason is that the center of gravity of the liquid will rise, so the B ball does more work externally, and the state of the two balls is the same, so the B ball needs to absorb more energy 4. Conservation of momentum is something that all objects that collide with each other have to obey it, and mechanical energy doesn't necessarily produce heat at the moment of collision, and that's the part you wonder about.

1.Because there is atmospheric pressure in the outside world, the increase in the volume of water must indicate that the water exerts force on the outside, so the water does work on the outside; 2。Note that both experiments say that the bullet passes through the block, indicating that the internal energy of the block is due to the bullet, so that e1 = e2 is transformed by the mechanical energy of the bullet and has nothing to do with the interaction time.

4。There is also part of the mechanical energy converted into the internal energy of the wooden block, if the internal energy is included, the total mechanical energy is equal to the mechanical energy of the original bullet; Momentum is mv, not energy (the physical quantity is different), it is another law independent of the law of conservation of energy, it has nothing to do with mass and velocity, not energy, and of course it has nothing to do with "finally moving together".

The second question, first of all, they have to pass through the wooden block, the first wooden block is fixed, there will be no speed, relatively stationary, the time is shorter, the second block is not fixed, it will produce speed, they are not relatively stationary, it will take longer! As for the use of equality: mv1=(m+m)v2 is the conservation of momentum, their final velocities are equal, and then use the formula of conservation of energy!

In your second year of high school, you won't even know the formula for conservation of energy, right?

It's easier to buy a textbook and copy it yourself, and there are explanations in it.

Intensity x vertical area = magnetic flux.

Hence b==

It's actually quite simple.

Power = 10% * total power (i.e. wind kinetic energy per unit time) Wind kinetic energy per unit time = 1 2 * (wind mass per unit time) * square of wind speed per unit time wind mass = t [(per unit time) (can be expressed by 1)] * wind speed * s [(i.e. the area of a circular surface of 12 meters) (this is the force surface)] * density of air.

Substitution can be solved.

I switched to physics questions, and only wrote about the ideas I didn't understand, and I hope to forgive me.

It can be done using the unit method The unit of power is w p = f * v f and is equal to the mass multiplied by the acceleration, that is, kg*m s 2 so the total is kg*m 2 s 3 See no Now the units appear in the problem It is to ask you what you know m s , kg m 3 , m how to get it kg*m 2 s 3 is obviously (m s) 3 * kg m 3 * m 2 Of course, notice that this is the radius, since the square must be multiplied by the area, that is, p = 125* *1 2