What are the seven basic units of the international system of units

The name of the unit of physical quantity and the symbol of the unit
Length (L) M
Mass (m) kg
Time (T) s
Current (I) a
Thermodynamic temperature (T) Kelvin K
The amount of matter is (n) mol
Luminescent intensity (LV) candela CD

On a rough horizontal plane, there are two pieces of wood 1 and 2 with mass M1 and M2 respectively. In the middle, they are connected by a light spring with original length L and stiffness coefficient K. the sliding friction coefficient between the block and the ground is u. first, pull the block 2 to the right with a horizontal force. When the two blocks move at a uniform speed, what is the distance between the two blocks? M2 is useless, which is no different from pulling M1 directly with a spring
Analyze M1 force, spring force and friction force, two force balance
Friction um1g = elastic force = kx
x=um1g/k
The distance is L + um1g / K, why it has nothing to do with M2!

In the process, it can be found that M2 will be naturally eliminated
M 2 is subjected to friction u m 2G, spring tension k x and horizontal force F, where f = k x + U M 2G. (1)
Taking M1, M2 and spring as a system, the force of the system is analyzed. The system is only subjected to horizontal force F and friction um1g + um2g
There is f = um1g + um2g. (2). Substituting (1), we can find that M2 is eliminated, and we get
um1g=kx.(3)
The solution of the original problem

How many Mu is one square kilometer

One mu is equal to 666.67 square meters

Find a solid metal ball, use a spring dynamometer to measure 54 n outside the gravity in the air, immerse it in water, the test number of spring scale is 34 n, find g = 10N / kg
What is the volume of a metal ball in cubic meters
What is the metal composition of the ball

1. The buoyancy of air is negligible,
The buoyancy of the metal ball in water f = G-F = 20n
From F floating = P liquid GV row, it can be seen that V row = f floating / P liquid g = 2.0x10 - & sup3; 3M & sup3;
2. From g = mg = PVG, P = g / VG = 2.7x10 & sup3; kg / M & sup3;

If the side length of a square is 3, and the area of the new square is y after the side length is reduced by X, then the analytic function of Y with respect to X is

Y=(3-X)²=X²-6X+9,
(0≤X≤3).

As shown in the figure, a light rope crosses the smooth fixed pulley, and two objects with mass M1 and M2 are attached at both ends. M1 is placed on the ground, and M2 is a certain height from the horizontal ground. When the mass of M2 changes, the acceleration a of M1 will also change. In the following four images, the most accurate relationship between a and M2 is ()
A. B. C. D.

When M2 ＞ M1, M1 has upward acceleration. According to Newton's second law, for M1: t-m1g = m1a & nbsp; & nbsp; for M2: m2g-t = M2A, a = M2 − m1m2 + m1g is obtained

The plan is negative and the actual completion is also negative. How to calculate the completion ratio

Negative number actually completed? Impossible

A box of potatoes on the turntable moves in a uniform circular motion with angular velocity ω. The mass of one potato in the middle position is m (can be regarded as a particle), and the distance from it to the rotating shaft is R. then the force of other potatoes on the potato is ()
A. m2g2+m2ω4R2B. mω2RC. mgD. m2g2−m2ω4R2

According to Newton's second law and the formula of centripetal force, there are: horizontal direction: FX = m ω 2R, vertical direction: FY = mg; so the resultant force is: F = FX2 + FY2 = m2g2 + M2 ω 4r2

In the known arithmetic sequence an, A3 = 7, a1 + A2 + a3 = 12, let BN = an × a (n + 1), the sum of the first n terms of sequence 1 / BN is TN, n ∈ n*
2 verification: TN < 1 / 3
3. Through the exploration of the sequence TN, write a true proposition of "T1, TM, TN are equal proportion sequence" and explain the reason (1 < m < n, m, n ∈ n *)

So 1 / BN = 1 / (3n-2) * (3N + 1) = 1 / 3 * [1 / (3n-2) - 1 / (3N + 1)], so TN = 1 / 3 * [(1 / 1-1 / 4) + (1 / 4-1 / 7) +. + (1 / (3n-2) - 1 / (3N + 1))] = 1 / 3-1 / [3 * (3N + 1)], so it is less than 1 / 33

There are two cars a and B on the straight road. A starts to drive from a standstill at an acceleration of 0.5m/s2, and B moves at a constant speed in the same direction at a speed of 5m / s 200m in front of A. question: (1) when will a catch up with B? How fast does a catch up with B? How far is a from the starting point? (2) In the process of catching up, when is the maximum distance between a and B? What is the distance?

(1) When a overtakes B, the difference of their displacements is x0 = 200m, & nbsp; x a = x0 + X B. let a overtake B with time t, then x a = 12a a T2, x B = v b T. according to the condition of overtaking, there is 12a T2 = v b t + 200, and the solution is t = 40 & nbsp; s or T = - 20 & nbsp; s (rounding off). Then the velocity of a is v a = a T = 0.5 × 40 & nbsp; m / S = 20 & nbsp; s; M / s, x a = 12a, T2 = 12 × 0.5 × 402 & nbsp; m = 400 & nbsp; m. (2) in the process of catching up, when a's speed is less than B's, the distance between a and B is still increasing, but when a's speed is greater than B's, the distance between a and b decreases. When the two speeds are equal, the distance between a and B reaches the maximum. From a a T = v b, t = 10 & nbsp; s, that is, a is at 10 & nbsp; s; Xmax = x0 + V B t-12a a T2 = (200 + 5 × 10-12 × 0.5 × 102) & nbsp; m = 225 & nbsp; M. (1) a catches up with B in 40s, and the speed of a catches up with B is 20 & nbsp; m / s, at this time a is 400 & nbsp; m from the starting point. (2) in the process of catching up, there is a maximum distance between a and B at 10 & nbsp; s, which is 225 & nbsp; M

What are the seven basic units of the international system of units