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The length of train a and train B are 144 meters and 180 meters respectively, and train a travels 4 meters more per second than train B. (1) it takes 9 seconds for the two trains to travel in opposite directions, from meeting to completely staggering. What's the speed of the two East trains? (2) if they travel in the same direction, how many seconds does it take for the head of train a to catch up with the tail of train B to completely overtake train B?
If x + (x + 4) × 9 = 144 + 180, then x is 16 and a's speed is 20
The length of train a and train B are 144m and 180m, and train a runs 4m more per second than train B. the two trains are facing each other, and it takes 9s from meeting to staggering. What's the speed of the two trains?
Suppose car B travels XM per second, then car a Travels (x + 4) m per second. According to the meaning of the question, we get: 9 (x + X + 4) = 144 + 180, sort out: 2x = 32, solve: x = 16, then car a travels 20m per second, car B travels 16m per second
The two trains run from two places 450 kilometers apart and meet each other in five hours. It is known that the speed ratio of the two trains is 4:5. How many kilometers do the two trains travel per hour?
Let B's velocity be x km / h, and the equation: (x + 45x) × 5 = 450 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 9x = 450 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; X = 50, a's velocity is 50 × 45 = 40 (
The two trains run from two places 450 kilometers apart and meet each other in five hours. It is known that the speed ratio of the two trains is 4:5. How many kilometers do the two trains travel per hour?
Let B's speed be x km / h, and the equation can be obtained as follows: (x + 45x) × 5 = 450 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 9x = 450 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; X = 50. A's speed is 50 × 45 = 40 km / h. A's speed is 40 km / h, B's speed is 50 km / h
The construction site needs 400 m of sand and stone. If it is transported by trucks with a load of 4 T, how many trucks are needed? (the density of sand and stone = 2.6 × 10 kg / M),
400x2.6 × 10 ^ 3 = 1040000kg = 1040t
260 = 1044 / car
So we need to transport 260 cars
Which is more important, tree planting or forest protection
It's all important
The ratio of freight car speed to passenger car speed is 3:4. The two cars run from station a and B at the same time and meet at 6km away from the midpoint. How many kilometers is the distance between the two places
Formula and why!
Because the ratio of freight car speed to passenger car speed is 3:4, the ratio of two cars' journey is 3:4 when they meet, which is set as 3x and 4x respectively
Because the two cars met at 6km away from the midpoint, the bus went 6 + 6 = 12km more, so 3x + 12 = 4x, x = 12
The distance between a and B is 3x + 4x = 84km
Seek 20 rational mixed operation, which has a better power!
Our lovely old class homework! 5555 ~ to 20 rational number mixed operation oh! Hope that the formula can add a little power!
[-|98|+76+(-87)]*23[56+(-75)-(7)]-(8+4+3) 5+21*8/2-6-59 68/21-8-11*8+61 -2/9-7/9-56 4.6-(-3/4+1.6-4-3/4) 1/2+3+5/6-7/12 [2/3-4-1/4*(-0.4)]/1/3+2 22+(-4)+(-2)+4*3 -2*8-8*1/2+8/1/8 (2/3+1/2)/(-1/12)*(-1...
1. The construction site needs 400m3 of sand and gravel, which can be transported by 4T trucks. How many trucks do you need? (ρ sand = 2G / cm) look at my density, etc
The process is awesome! But the result is not so good! I'm just looking for process + correct answer now! I raised the reward to 100!
Hope to give me a satisfactory answer
Solution 400m ^ 3 = 4 × 10 ^ 8cm ^ 3
M sand = ρ v = 2G / cm × 4 × 10 ^ 8cm ^ 3
=800t
N = 800t / 4T / vehicle = 200 vehicles
Two hundred
2g/cm³=0.5x10³kg/m³
400m³x500kg/m³=200000kg
4t=4000kg
200000/4000=50
A: we need to transport 50 cars
Density = 2000kg / m3, so a car pulling 2m3 shares 400 / 2 = 200
P = 2600kg / m3 v = 400m3
M = PV = 2600kg / m3 * 400m3 = 1040t
1040t / 4T = 260 cars
400 cubic centimeters or 400 cubic meters?
If it's a cubic centimeter, one car is enough.
If it is cubic meters, it needs to be substituted into the density calculation of sand.
Generally, the density of sand is 2.5g/cm3. For this calculation, there are about 400 * 2.5/4 = 250 vehicles.
The density of sand is
It is 2500kg / m3
So from the formula P = m / V
The obtained quality is
1*10^6KG=1*10^3t
250 cars
LZ: stone density is usually 2400 ~ 2800
If it's 2600
260 cars
ρ sand = 2 g / cm = 2T / M & # 179;
Total weight of sand and stone m = 400m & # 179; X 2T / M & # 179; = 800t
4 tons at a time
800/4=200
So, 200 cars
The density of sand is
2500kg / M
So from the formula P = m / V
The obtained quality is
1*10^6KG=1*10^3t
250 cars
LZ: stone density is usually 2400 ~ 2800
If it's 2600
260 cars
LZ's stone is too light,
It is known that v = 400m, M = 4x10 cubic kg density = m / v = 4x10 cubic kg / 400m = 10kg / m, 10kg / M density of sand removal is 2.6, so the month is three vehicles
In 2009, 500 million trees were planted to conserve 300 million cubic meters of water. By 2015, the construction of "forest city" will be completed,
That is, trees can maintain 1.1 billion cubic meters of water for a long time
1. In the seven years from 2009 to 2015, the city planted a total of 100 million trees?
2. If 2009 is taken as the first year, and the capacity of water conservation y (100 million cubic meters) is set as the first function in the x year, the analytic formula of the function is obtained, and the analytic formula of the function is obtained, and how much water can be conserved in the third year (that is, 2011)?
1. Each tree can conserve 3 / 5 cubic meters of water. If there are x billion trees in 2015, then 3 / 5 * x = 11 and x = 55 / 3, then there are 55 / 3-5 = 40 / 3 trees planted during this period
2. A total of 40 / 3 trees are planted in 6 years. If 40 / 3 trees are planted every year divided by 6 = 20 / 9, then y = 3 / 5 * (5 + 20 / 9 * (x-1))
Bring x = 3 into 17 / 3
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