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The resistance experienced by the bullet when it enters A is A, the interaction force with the bullet. And the time is extremely short, so the bullet, a momentum is conserved.

Let the internal energy generated by : e, and when the bullet stops in a, the velocity equal to a is :v1, then there is:

v1=0m/s

Conservation of energy: e+ (

e= j and the spring force can be regarded as the internal force of the system.

Therefore, after the bullet is fired, the momentum of the system composed of the bullet and a and b is conserved.

Whereas, when the velocity is equal, the spring has the maximum potential energy.

Let the maximum elastic potential energy be: ekmax

v2=-5m/s

Conservation of energy: ekmax=1*10*10 2-(

The electric field force is independent of the work done and the path, i.e. the distance, but only the initial and final positions (i.e., the displacement), and there are two electric fields here. So if you write an expression where x is the distance in the left electric field, the expression is wrong.

The parsing process is as follows:

1. Determine where the slider finally stops.

In the right electric field, if the velocity of the slider is 0, then in the horizontal direction, it is obvious that the net force is not 0, there is an electric field force qe, so it is impossible for the slider to stop in the right electric field. As shown below:

In the left electric field, if the speed of the slider is 0, its maximum static friction force is f, according to e=3f q, it can be seen that the electric field force is: qe=3f, obviously in the horizontal direction, the net force of these two forces is not 0, so it is impossible for the slider to stop in the left electric field, as shown in the figure below:

Based on the above analysis, the slider can only stop at a in the end.

2. The kinetic energy theorem is used for the whole process of the slider.

Note: The electric field force work is independent of the path, because the starting position of the slider is at a, and the final position is also at a, so the displacement of the slider is 0, so the electric field force on the left and right sides does the work.

The work done by sliding friction is related to the path, that is, to the distance, so the frictional force is work, and its work is: w=-fx, where x is the distance in the left electric field.

According to the kinetic energy theorem there is: -fx=0-mv0 2. The distance of the slider in the left electric field x can be solved.

In the third question, the increase in electric potential energy cannot be multiplied by x

Your x is the distance of the left movement, but the effective displacement of the work of the electric potential energy cannot be the distance of the left side, it must be the displacement.

Since it is inconvenient to write, I will give you a general description of the process of solving the problem. Because the shrapnel can not fall in the circumference of the required radius, then the shrapnel is required to have an initial velocity, and the shrapnel has to do a flat throwing motion, so as long as you know the height of the shrapnel, you can find the minimum initial velocity of the shrapnel according to the formula of the flat throwing motion. And you know the velocity of the shell at the beginning, and he does an upward throwing motion, and it is easy to find the height of the shell, and then you can also find the initial velocity of the shrapnel in question.

This shrapnel weighs 4kg, then the other shrapnel is 2kg, and the two of them should conform to the momentum theorem, that is, the total momentum of the two of them is zero (the shell is considered stationary at the highest point). That's when you can find the velocity of another shrapnel. Now that you know the mass and velocity of the two shrapnel, it's easy to find their total kinetic energy.

The key is to analyze that the beginning is an upward sell, followed by a flat sell, which conforms to the momentum theorem at the highest point.

1. x=v1*t=3t 1).

y=1 2*a*t 2=t 2 2) subtract t to get y=1 9*x 2

2. When arriving at the other side of the river, y=d=100m, obtained by formula (2), crossing time t1=10s, obtained by formula (1), x=30m, and walking time t2=20 2=10s

Shared 20s.

1.The trajectory equation is an expression of displacement, this and the flat throwing motion is about the same, on the x-axis, displacement = v1t, on the y-axis, displacement = at square 2

The combined displacement is: x = (v1t) square under the root number + (at square) can be simplified, pay attention to the value range of time t.

2.First, use the river width to calculate the river crossing time, that is: 100 = at square 2, and then calculate the displacement of people in the x direction during this time, and then the time for people to walk is: 50-x direction displacement = 2 t1

Calculate t1 to calculate the total time is t+t1