Xiaoming starts from a at 8 a.m. and goes to B at 20 kilometers per hour. 15 minutes later, Xiaogang starts from a and goes to B at 16 kilometers per hour In B, Xiao Ming takes a 60 minute rest in B and then returns to A. on the way back, he meets Xiao Gang from A. at this time, they are 2 kilometers away from B. find the distance between a and B

Xiaoming starts from a at 8 a.m. and goes to B at 20 kilometers per hour. 15 minutes later, Xiaogang starts from a and goes to B at 16 kilometers per hour In B, Xiao Ming takes a 60 minute rest in B and then returns to A. on the way back, he meets Xiao Gang from A. at this time, they are 2 kilometers away from B. find the distance between a and B

Suppose the distance between AB and ab is x km, and the total distance Xiao Ming has traveled is (x + 2) km, then the total time Xiao Ming has experienced from starting to meeting Xiao Gang is [(x + 2) / 20 + 60 / 60] hours, so the total time Xiao Gang has experienced is [(x + 2) / 20 + 60 / 60] - 15 / 60 hours, so we can get the distance Xiao Gang has traveled and the distance a from the meeting point

At the sports meeting, Xiao Ming, Xiao Gang and Xiao Qiang all took part in the 1500 meter race. Xiao Ming and Xiao Qiang are 113 meters apart, Xiao Gang and Xiao Qiang are 201 meters apart. How many meters are Xiao Ming and Xiao Gang apart? How to calculate

113 + 201 = 314 or 201-113 = 88

Xiao Ming and Xiao Gang are walking from two places at the same time. The distance between the two places is 26 kilometers. Xiao Ming walks 7 kilometers per hour and Xiao Gang walks 6 kilometers per hour. If Xiao Ming takes a dog and he starts at the same time, the dog runs to Xiao Gang at the speed of 10 kilometers per hour. When he meets Xiao Gang, he immediately runs to Xiao Ming. When he meets Xiao Ming, he immediately runs to Xiao Gang It ran backwards until the two met, and the dog ran thousands of meters

26 (7 + 6) = 2 (hours), which is the time Xiaoming and Xiaogang met,
2 × 10 = 20 km, which is the total distance the dog runs in 2 hours

Xiaoming and Xiaogang are 20 kilometers apart, Xiaoming is in front, Xiaogang is behind, Xiaoming walks for 2 hours first, and then two people walk together, Xiaoming 9 km h, Xiaogang 7 km H
When will Xiao Ming catch up with Xiao Gang

2 + (20-2 * 7) / (7 + 9) = 3 hours
Xiao Ming catches up with Xiao Gang in 3 hours

A few calories is a kilo

Calories are calories, not directly proportional to a kilo of fat
Calorie is defined as the amount of heat needed to raise 1 gram of water by 1 degree centigrade at 1 atmospheric pressure
"15 degree calories" for nutrition: the amount of heat required to raise 1 gram of water from 14.5 ℃ to 15.5 ℃ at 1 atmospheric pressure is about 4.1855 joules
Compared with our daily intake of calories, the measurement of "calories" is still too small. At present, nutrition generally adopts another unit "kcal" (kcal or C, also known as "large calorie") evolved from "calories". 1 kcal equals 1000 calories, about 4186 joules. The calories of fat are about 9 kcal / g; the calories of sugar and protein are only 4 kcal / g

If x ^ 2-13x + 1 = 0, then the digits of x ^ 4 + 1 / x ^ 4 are
Urgent, please answer in 30 minutes,

x^2-13x+1=0
x^2+1=13x
Divide both sides by X
x+1/x=13
Square on both sides
x^2+2+1/x^2=169
x^2+1/x^2=167
Square on both sides
x^4+2+1/x^4=167^2
x^4+1/x^4=167^2-2
The one digit number is seven

The hallway of the dormitory in the school uses the electric lamp marked "220V 25W" to light all night. In the middle of the night, due to the reduction of the total power consumption, the voltage of the power supply line can rise by 230V. The bulb is very easy to damage. A student wants to connect a resistor R to the bulb
When connected to the power supply line, it can prolong the life of the bulb
(1) After connecting a resistor in series, when the power supply voltage is 230V, the voltage at both ends of the bulb is still 220V
What is the resistance value of this resistance R
(2) The power supply voltage of 220 V is the electric power consumed by the series circuit R?
(3) Power supply voltage back to 220 V is the actual power of the bulb after re intervention resistance will change?
This is explained by the relevant formulas learned
I don't know if this question is wrong
If it's wrong, you can change it a little and then answer it in detail

That's right
1. Rated current of electric lamp I = P / u = 25 / 220 = 5 / 44a
Therefore, the current in series with the resistor is 5 / 44a, and the voltage on the resistor is 230-220 = 10V
So the resistance R = u / I = 10 / (5 / 44) = 88 Ω
Resistance consumption power P = u * I = 10 * 5 / 44 = 25 / 22W
When the power supply voltage is restored to 220 V, the actual power of the bulb will be smaller after it is re intervened into the resistor

When an object is moving in a straight line with uniform acceleration, the initial velocity is 0.5m/s, and the displacement in the 7th s is 4m more than that in the 5th s, the following results can be obtained: (1) the acceleration of the object; (2) the displacement of the object in the 5th s

(1) Using the formula of displacement difference in adjacent equal time: △ x = at2, it is obtained that: a = X7 − x52t2 = 42 = 2m / S2 (2) the displacement of the object in 5S is: x = v0t + 12at2 = 0.5 × 5 + 12 × 2 × 25 = 27.5m A: (1) the acceleration of the object is 2m / S2; (2) the displacement of the object in 5S is 27.5m

Junior high school physics concept formula review answer

This website can do exercises, online, with answers, very good

A small ball of mass m is tied to one end of the light rope. The other end of the rope passes through a small hole on a smooth horizontal table and is held by hand. First, the ball is driven at an angular speed
W1 makes a circular motion with the radius of R1 on the table, and then slowly pulls down the rope to reduce the radius to R2. In this process, what is the kinetic energy increment of the ball?

In the process of pulling, the force and moment are on the same line, that is, the impulse moment is 0, and the angular momentum is conserved
mr1^2w1=mr2^2w2
w2=(r1^2w1)/r2^2
v2=w2*r2
E=0.5mv2^2
I really don't know how to read the chapter about angular momentum in the book. That's right