How to do this physics problem in volume one of grade eight? 1. The distance between a and B is 900km. A train departs from a to B at 7:30am, stops at several stations and arrives at B at 16:30am on the same day (1) What's the average speed of the train from place a to place B? Kilometers per hour (2) What's the length of the train

1) 900km / (16:30-7:30) = 900km / 9h = 100km / h, the average speed of the train from place a to place B is 100km / h. 2) when the train runs through the bridge with 400m length at 144km / h, the length of the train is XM [(x + 400) / 1000] / 144 = 25 / 360036x + 14400 =

The supersonic anti-ship missile "Feilong 7" developed by our country can be launched from an aircraft and can fly at a speed higher than the sound speed. Its speed can reach 500m / s and its range is 32km. Because it is very close to the enemy ship, it is difficult to intercept. If it is used to attack the enemy ship at 15km, how much defense time does the enemy ship have at most?

The distance between the missile and the enemy ship is s = 15km = 103m × 15 = 1.5 × 104m; the defense time of the enemy ship is t = SV = 1.5 × 104m, 500m / S = 30s

Given that the image of quadratic function passes through (0,0), (1, - 1), (- 2,14), find the analytic expression of the quadratic function

Let the analytic expression of this quadratic function be y = ax & # 178; + BX + C
By substituting the coordinates of (0,0), (1, - 1), (- 2,14), we get
{c=0
a+b+c=-1
4a-2b+c=14
The solution is: {a = 2
b=-3
c=0
So, the analytic expression of this quadratic function is y = 2x & # 178; - 3x

If the polynomials x3-2x2-4x-1 and (x + 1) (x2 + MX + n) are equal regardless of the value of X, find the value of M and n

∵ polynomials x3-2x2-4x-1 and (x + 1) (x2 + MX + n) are equal, ∵ x3-2x2-4x-1 = (x + 1) (x2 + MX + n) = X3 + (M + 1) x2 + (n + m) x + N, ∵ m + 1 = - 2, n = - 1, M + n = - 4, ∵ M = - 3, n = - 1

If the length of a rectangle is increased by 2 cm, the area will be increased by 10 square cm. If the width is decreased by 3 cm, the area will be decreased by 18 square cm. Find the area of the original rectangle

The original width is 10 / 2 = 5 (CM); the original length is 18 / 3 = 6 (CM); the area of the rectangle is 6 × 5 = 30 (cm 2). Answer: the original area of the rectangle is 30 cm 2

If y is proportional to x, and x = root 3-1, y = root 2, then the function between Y and X is?

Y is proportional to X
y=kx
When x = radical 3-1, y = radical 2
√2=﹙√3－1﹚k
k=√2／﹙√3－1﹚＝√2×﹙√3＋1﹚／2=﹙√6＋√2﹚／2
y=﹙√6＋√2﹚／2x

Y = x (3lnx + 1)
How to derive with brackets
Open the derivation and I'll find y '= 3lnx + 4
The derivation method with brackets is that of U

Y = u * V, then y '= u' * V + U * V '
Take the formula: y '= (x * (3lnx + 1))' = x '* (3lnx + 1) + X * (3lnx + 1)' = 1 * (3lnx + 1) + X * (3 / x) = 3lnx + 4

As shown in the figure, the cross section of the tunnel is composed of parabola and rectangle. The length of the rectangle is 8m and the width is 2m. Parabola can be used
Y = - 1 / 4x & sup2; + 4 denotes
1) A freight truck is 4m high and 2m wide. Can it pass through the tunnel?
(2) If there is a two-way road in the tunnel, can the freight car pass through?
For detailed answers, it's better to have the correct format and be urgent,

When y = 0, x = 4, which coincides with 8M. When the rectangular bottom is the x-axis, the equation is
y=-1/4x²+6
1) The truck goes through the middle
X = 1, y = 5.75 > 4
2) The truck passes on the right side of the y-axis
X = 2, y = 5 > 4 can be passed

Given that f (x) is a quadratic function, if f (0) = 3 and f (x + 1) = f (x) + 2x-1, try to find the expression of F (x)

Let f (x) = ax & # 178; + BX + C
∵f(0)=3
∴c=3
And ∵ f (x + 1) = f (x) + 2x-1
∴a(x+1)²+b(x+1)+3=ax²+bx+3+2x-1
(2a-2)x+(a+b+1)=0
∴2a-2=0
a+b+1=0
∴a=1
b=-2
∴f(x)=x²-2x+3

Given that M is a root of the equation x with square-4x-4 = 0, then the square-4m of the algebraic expression m is______ .

The square of x-4x-4 = 0
x^2-4x=4
m^2-4m=4