The school bought 240 literature and art books, of which literature and art books are 2 / 3 of story books and story books are 3 / 4 of science and technology books. How many science and technology books did the school buy

The school bought 240 literature and art books, of which literature and art books are 2 / 3 of story books and story books are 3 / 4 of science and technology books. How many science and technology books did the school buy

If the science and technology book is x, there are:
2 (3x / 4) / 3 = 240 x = 480

There are 520 story books and literature and art books in the library, of which the number of literature and art books is 5 / 8 of that of science and technology books. How many literature and art books and story books are there respectively? (solution to the equation)

962411975,
There are x science and technology books and 5 / 8 x literature and art books
X＋5/8 X＝520
X＝520÷13/8
X = 320. 320 science and technology books
5 / 8 x = 5 / 8 × 320 = 200

There are 200 story books in the library. Story books are one fourth more than science and technology books

200=x+1/4x
X = 160 copies

There are 400 science and technology books in the library, three eighth less than story books. How many books are there on purpose

Let x (1-3 / 8) = 400, then x = 640

When the car is running at a speed of 9 m / s, it decelerates and moves straight until it stops. If the displacement of the car in the second second second after braking is 6 m, what is the displacement in the fifth second after braking?

Suppose the acceleration of the car is a, then the displacement x = (v0t2 + 12at22) - (v0t1 + 12at12) in the second second second is substituted into the data solution, a = - 2m / S2, the time for the car to brake to stop t0 = 0-v0a = 4.5s, so the displacement in the fifth second second is equal to the displacement in the last 0.5s. Taking the reverse thinking, X '= 12At'2 = 12 × 2 × 0.25m = 0.25m

Junior high school physics mechanics formula summary (detailed and comprehensive),

Speed: v = s / T
Density: ρ = m / V
Gravity: g = mg
Pressure: P = f / S
Buoyancy: F floating = g row = ρ liquid GV row
Floating: F = g
Lever balance condition: F1 × L1 = F2 × L2
Work: w = FS
Power: P = w / T = FV
Mechanical efficiency: η = w useful / W total = GH / Fs = g / FN (n is the number of strands of pulley block)

A spring vibrator with mass of M and stiffness coefficient of K makes a simple harmonic vibration with amplitude of A. when the weight passes through the balance position and moves in the specified direction, the timing starts. The vibration equation is

What can molecular current hypothesis explain?
A. The cause of magnetic field produced by electrified wire
B. Magnetization of soft magnetic rod
C. The reason of the interaction between two electrified conductors
D. The reason of magnetic field acting on moving charge

It should be the molecular circulation hypothesis
The electrons in molecules or atoms move around the nucleus to produce a molecular magnetic element. The circulation directions of all molecules are the same. Because the adjacent circulation directions are opposite, they cancel each other, which is equivalent to a ring current (binding current) on the surface of the object, thus producing a magnetic field
It can be used to explain the phenomenon of magnetization

The spaceship is completely weightless. Why can't the spring dynamometer measure gravity

Weightlessness means the loss of part (or all) of gravity. Complete weightlessness means the loss of all gravity. When gravity is zero, the spacecraft is completely weightless, which means that the spacecraft, including the objects on it, loses all gravity, so the spring dynamometer can't measure gravity

1. Add water to a cylindrical bucket with a diameter of 80cm and a height of 60cm. The volume of water in the bucket is between V (CM & # 179;) and the height of water surface x (CM)
The function expression for is________________ Where the constant is_______ The variable is_______ The value range of the independent variable is______ .
2. Find the value range of the following function independent variable X:
(1) Y = radical 5-3x; (2) y = x + 1 / X & # 178; - 2x-3; (3) y = radical X-2 / X & # 178; - 9

（1）
V=π×(80/2)²×x=1600πx (0≤x≤60)
The function expression is v = 1600 π X
The constant is 1600 π, the variable is x, and the value range of independent variable is 0 ≤ x ≤ 60
（2）
If 5-3x ≥ 0, X ≤ 5 / 3
If X & # 178; - 2x-3 ≠ 0, then x ≠ 3 and X ≠ - 1
If X-2 ≥ 0 and X & # 178; - 9 ≠ 0, then x ≥ 2 and X ≠ 3