Composition in unit 2 of Chinese Book Volume 2 of grade 4

Composition in unit 2 of Chinese Book Volume 2 of grade 4

Fourth grade volume two Chinese unit 2 composition, short!
No, thank you!

Mom, mom, I have a lot of words I want to say to you, but I don't have the courage. I also know that you may scold me before I say it. I have been wronged all the time. This time I borrow the composition we are going to write to tell you! I don't know why, I always think you are eccentric, you always

The mass relation of two objects a and B is Ma = 2MB. There is a compression spring in the middle, which is placed on a smooth horizontal plane. Now it is released from rest at the same time for a short period of time
A. The velocity of a is half of that of B. the momentum of a is greater than that of C. the force of a is greater than that of D. the total momentum of the system is 0

Total momentum is conserved. Momentum is equal in magnitude and opposite in direction. D is right. B is wrong
All forces are provided by springs, so the forces are equal. C error
ma.va + mb.vb=o . a correct
So the answer is ad

How is 4 5 9 1 equal to 24

4-1=3
3×5=15
15+9=24
Ask for praise

The dynamic friction coefficient between the object with mass m and the horizontal plane is μ. Now the oblique upward force F at an angle of θ with the horizontal plane is used to pull the object. The distance of the object moving at a constant speed along the horizontal plane is L. try to find the work done by the pulling force in this process

Work = force * displacement in the direction of force
The work done by the pulling force w = flcosq
If f is an unknown quantity, we need to find F first
f=u(mg-FsinQ)
Uniform velocity, horizontal force balance
FcosQ=f=umg-uFsinQ
F=umg/(cosQ+usinQ)
The work done by the pull f is
W=FLcosQ
=umgL(cosQ)/(cosQ+usinQ)

If A2 + A4 + A6 = 12, then the value of S7 is ()
A. 21B. 24C. 28D. 7

∵ A2 + A4 + A6 = 12, ∵ A2 + A4 + A6 = 12 = 3A4 = 12, that is, A4 = 4, then S7 = 7 (a1 + A7) 2 = 7 × 2a42 = 7a4 = 7 × 4 = 28

When an object moves in a straight line with uniform speed change, the timing starts from a certain moment, i.e. t = 0, and the displacement of the object passing through in two consecutive 2S is 8m and 16m respectively. Find out: (1) the acceleration of the object; (2) the velocity of the object when t = 0

(1) According to △ x = at2, a = △ XT2 = x2 − x1t2 = 84m / S2 = 2m / S2. (2) from X1 = v0t + 12at2, 8 = 2v0 + 12 × 2 × 4, V0 = 2m / s

Dad takes a day off every 6 days and mom takes a day off every 7 days. If Dad and mom take a day off at the same time on March 4, where will they take a day off at the same time next time

They will have a rest on April 29 next time. Thinking: they will have a rest every (6 + 1) * (7 + 1) = 56 days. Last time they had a rest on March 4, and next time they will have a rest on April 29 after 56 days

(about integers)
When calculating integral subtraction a - (A & sup2; + 2bc-5b & sup2;), Xiao Mahu mistakenly regards the title as a + (A & sup2; + 2bc-5b & sup2;), and the result is 3A & sup2; - 2BC + 7b & sup2;. Can you help Xiao Mahu find the correct result of this problem?
LZ, thank you very much

Analysis: first find a, then substitute a + (A & sup2; + 2bc-5b & sup2;) = 3A & sup2; - 2BC + 7b & sup2;, then a = 2A & sup2; - 4bc + 12b & sup2; substitute a into a - (A & sup2; + 2bc-5b & sup2;) = 2A & sup2; - 4bc + 12b & sup2; - (A & sup2; + 2bc-5b & sup2;) = A & sup2; - 6BC + 17b & sup2

It is known that the sum of the squares of the two equations X & # 178; + (2k + 1) x + K & # 178; - 2 = 0 is less than 10 times of the product of the two, so we can find K

See figure