As shown in the figure, the masses of the two wooden blocks are m and m, and the stiffness coefficient of the middle spring is K. the lower end of the spring is connected with m, and M is not connected with the spring. Now press m down for a certain distance to release it, and it will move harmoniously up and down. In the process of vibration, m never leaves the spring. Try to find: (1) the maximum amplitude of M vibration; (2) the maximum pressure of m on the ground when m vibrates with the maximum amplitude

As shown in the figure, the masses of the two wooden blocks are m and m, and the stiffness coefficient of the middle spring is K. the lower end of the spring is connected with m, and M is not connected with the spring. Now press m down for a certain distance to release it, and it will move harmoniously up and down. In the process of vibration, m never leaves the spring. Try to find: (1) the maximum amplitude of M vibration; (2) the maximum pressure of m on the ground when m vibrates with the maximum amplitude

(1) In the equilibrium position, let the compression of the spring be x0: kX0 = mg. In order to keep m from leaving the spring in the process of vibration, the highest point of M vibration can not be higher than the original strength of the spring, so the maximum amplitude of M vibration is a = x0 = MGK (2) M. when the vibration reaches the lowest point with the maximum amplitude A, the compression of the spring is the maximum

The four numbers of 2, 3, - 4 and - 9 (each number can only be used once) are used for "+, -, ×, △ four operations. Please list a formula to make the result better______ =24．

It can be (- 4) × (- 9) △ 3 × 2 = 24

The dynamic friction coefficient between the object with mass m and the horizontal plane is u. the force at an angle a with the horizontal plane is used to pull the object to make the object move at a uniform speed s along the horizontal plane,
The work done by this force on an object is (the answer is umgscosa / (COSA + usina))

Fx=Fcosa
Fy=Fsina
f=u(mg-Fy)=u(mg-Fsina)
Uniform speed, balanced force
f=Fx
u(mg-Fsina)=Fcosa
F=umgcosa/(cosa+usina)
The work done by a force on an object is
W=umgscosa/(cosa+usina)

The sum of the first n terms of the arithmetic sequence {an} is SN. If A2 + A4 + A6 = 12, then the value of S7 is______ ．

According to the properties of arithmetic sequence, we can get A2 + A4 + A6 = 3A4 = 12, the solution is A4 = 4, ∧ S7 = 7 (a1 + A7) 2 = 7 × 2a42 = 7a4 = 7 × 4 = 28, so the answer is: 28

The displacement of a particle moving at constant speed is 8m in the first 2S and 20m in the second 2S. The initial velocity and acceleration of the particle are calculated?

From △ x = at2, we can get: acceleration is a = 20 − 822m / S2 = 3m / S2; for the first 2S, we have: X1 = v0t + 12at2 solution: V0 = X1 & nbsp; − 12at2t = 8 − 62m / S = 1m / S; answer: acceleration of particle motion is 3m / S2; initial velocity is 1m / s

From April 1, Xiao Hong's mother took a day off every four days, and his father took a day off every six days,
When can Xiao Hong's family go to the park together

I knew it was 12 days later, April 13
Divide by simple

In order to attract customers, supermarkets A and B sell the same goods at the same price. In order to attract customers, they offer different preferential schemes: after supermarket a has purchased more than 300 yuan, the excess part will be given a 20% discount at the original price; after supermarket B has purchased more than 200 yuan, the excess part will be given a 50% discount at the original price, and the customer is expected to purchase X Yuan (x > 300) (1) When x = 400 yuan, which supermarket will you go to? (2) When x is the value, the actual amount of money spent by the two supermarkets is the same?

(1) The cost of shopping in a supermarket is: 300 + 0.8 (x-300) = (0.8x + 60) yuan, the cost of shopping in B supermarket is: 200 + 0.85 (X-200) = (0.85x + 30) yuan; when x = 400, the cost of shopping in a supermarket is: 0.8 × 400 + 60 = 380, the cost of shopping in B supermarket is: 0.85 × 400 + 30 = 370, so there is a discount in B supermarket; (2) according to the meaning of the title From (1): 300 + 0.8 (x-300) = 200 + 0.85 (X-200), the solution is: x = 600, a: when x = 600, the two supermarkets spend the same amount of money

Given the roots of the equation x & # 178; - (K + 1) x + 1 / 4K & # 178; + 1 = 0 about X, we can find the value of K according to the following conditions. (1) the product of two equations is equal to 5
(2) Equation x1.x2 satisfies lx1i = X

(1) The product of two equations equals five
b^2-4ac= (k+1)^2-4(1/4 k^2 +1)≥0,2k-3≥0,k≥3/2
X1 * x2 = C / a = 1 / 4, K ^ 2 + 1 = 5, K ^ 2 = 16, k = 2 or - 2,
So, k = 2
(2) The equation x1.x2 satisfies lx1i = x, which cannot be seen clearly

For two math problems, we need to use addition, subtraction and elimination,
System of linear equations with three variables: (there must be a process and an answer, and the method of addition, subtraction and elimination should also be used.)
① {x+y+z=4
3x+y-2z=0
2x+3y+z=7
② {3x+2y+5z=2
x-2y-z=6
4x+2y-7z=30

① If {x + y + Z = 4, ① 3x + y-2z = 0, ② 2x + 3Y + Z = 7, ③ 1 × 2 + 2, we get 5x + 3Y = 8, ④ 3 × 2 + 2, 7x + 7Y = 14, ⑤ 5, we get x + y = 2, ⑥ from 6, x = 2-y, ⑦ from 7 to 4, y = 1 from y = 1 to 7, x = 1 from y = 1, x = 1 from x = 1 to 1, we get z = 2

The sequence {an} is an equal ratio sequence, A3 + A7 = 20, A1 · A9 = 64, find the value of a11

Because an is an equal ratio sequence, A1 · A9 = (A5) = 64, because A3 + A7 = 20 > 0, A5 > 0, A5 = 8, so A3 = 8 / Q, a7 = 8q, so (8 / Q) + 8q = 20, so q = 0.5, a11 = A5 · Q6 = 8 × (0.5) = 1