Static friction and sliding friction Isn't the maximum static friction the horizontal thrust of an object at the moment when it is about to move? Then the friction becomes smaller when the object gets up? Besides, doesn't sliding friction require the object to move relatively? If the thrust of the object is less than sliding friction, how does it move, A thing weighs 500N, the maximum static friction is 300N, and u is 0.56. One asks how much force is given to keep it moving at a constant speed when it moves, and how much sliding friction is given to push it 200N until it stops? The answers are all 280n. What's the matter? 200N is smaller than 280n. How does it move?

Static friction and sliding friction Isn't the maximum static friction the horizontal thrust of an object at the moment when it is about to move? Then the friction becomes smaller when the object gets up? Besides, doesn't sliding friction require the object to move relatively? If the thrust of the object is less than sliding friction, how does it move, A thing weighs 500N, the maximum static friction is 300N, and u is 0.56. One asks how much force is given to keep it moving at a constant speed when it moves, and how much sliding friction is given to push it 200N until it stops? The answers are all 280n. What's the matter? 200N is smaller than 280n. How does it move?

Before an object does not move, to make it move, it must overcome the static inertia, so the static friction is relatively large;
Once it moves, it only needs to overcome the resistance that hinders the movement. The force that hinders the movement is sliding friction, so the sliding friction is relatively small
In order to maintain a uniform linear motion, the force required must be equal to the sliding friction, which should not need to be explained
As for the problem that the thrust is 200 N, the sliding friction is 280 n, and the object is still moving, it is like this: the object is moving first, and it will not stop at once. Because the resistance is greater than the thrust, the speed will certainly decrease, but no matter how the speed decreases, it will move before it becomes zero, but the speed is getting smaller and smaller

Can static friction and sliding friction do positive work

Yes
Static friction does positive work: when an object is placed on a stationary turntable, the turntable is not smooth. When the speed of the turntable is gradually increased, and the object remains relatively stationary with the turntable, the static friction on the object does positive work on the object, increasing the kinetic energy of the object
Sliding friction does positive work: the bicycle moves forward because the sliding friction of the ground facing the rear wheel moves forward, which makes the bicycle move forward. At this time, there is displacement in the direction of friction, and the sliding friction does positive work

Static friction and its relationship______ But when the static friction is equal to the sliding friction,
When an object starts to slide, the friction doesn't change

The static friction is related to the external force on the object
But when the static friction is equal to the sliding friction, the object begins to slide and becomes sliding friction, and the friction does not change

How to calculate 1 * 2 * 3 / 1 + 2 * 3 * 4 / 1 +... + 9 * 10 * 11 / 1?
1 1 1
------How much is + - - + · + - - -? It's a simple calculation
1*2*3 2*3*4 9*10*11

The original formula = (1 / 1) * [1 / (2 * 3)] + (1 / 2) * [1 / () 3 * 4] +. + (1 / 9) [1 / (10 * 11)]
=(1/1)*(1/2-1/3)+(1/2)*(1/3-1/4)+.+(1/9)(1/10-1/11)
=1/(1*2)-1/(1*3)+1/(2*3)-1/(2*4)+.+1/(9*10)-1/(9*11)
=[1/(1*2)+1/(2*3)+.+1/(9*10)]-[1/(1*3）+1/（2*4）+.+1/（9*11）]
=（1-1/2+1/2-1/3+.1/9-1/10）-（1/2）*[2/(1*3）+2/（2*4）+.+2/（9*11）]
=1-1/10-(1/2)*[1-1/3+1/2-1/4+1/3-1/5+1/4-1/6+.+1/8-1/10+1/9-1/11]
=1-1/10-(1/2)*（1+1/2-1/10-1/11）
=1-1/10-1/2-1/4+1/20+1/22
=27/110

On the number axis, the distance between M and N is 2012 (M is on the left side of n), and M12
What are the numbers represented by M and N? What's the reason
And the two points of Mn overlap each other after folding in (3).

The two points of ∵ Mn overlap each other after folding in (3),
The distance between M, N and 3 is equal, both are 1006,
∵ m on the left, ∵ M = - 1003,
∵ n is on the right, ∵ n = 1009

1 + 1 / 2 - 5 / 6 + 7 / 12 - 9 / 20 + 11 / 30 - 13 / 42 + 12 / 56

1 + 1 / 2 - 5 / 6 + 7 / 12 - 9 / 20 + 11 / 30 - 13 / 42 + 12 / 56
=1+1/2-5/6+7/12-9/20+11/30-13/42+12/56
=1+1/2-1/2-1/3+1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7+1/1/7+1/8
=1+1/8
=9/8

The tangent equation of the graph with function f (x) = 4x ^ 3 + ax ^ 2 + BX + 5 at x = 1 is y = - 12x

f(1)=4+a+b+5=-12
a+b=-21 --------------(A)
f'(x)=12x^2+2ax+b
f'(1)=12+2a+b=-12
2a+b=-24 -------------(B)
(a) and (b) respectively
a=-3, b=-18
f(x)=4x^3-3x^2-18x+5

How do two four and two six equal 24

Only add, subtract, multiply and divide can't calculate 24. I've checked it with computer

Finding the derivative of - x ^ 2 power of y = - e

y=-e^(-x^2)
y'=-e^(-x^2)*(-x^2)'=-e^(-x^2)*(-2x)=2x*e^(-x^2)
If you don't understand, please hi me, I wish you a happy study!

16 minus 1 / 4 of a number equals 12. What's the number

(16-12) △ 1 / 4
=4x4
=16
So the number is 16
I wish you progress in your study, you can ask if you don't understand! Thank you!