5 7, Physics, thank you 5

5.The concept of power and work needs to be strengthened, p=fv, for force, w=fs, w=pt, are an average concept, such as which direction of power is the product of the average force and average velocity acting on the object, the power is also the product of the average power and the displacement from this moment to that moment, for A and B, at the same time t1 has w B is greater than w A, for the same time t2 also has w B greater than w A, power is w t, that is, the slope of two straight lines, So the power of B is greater than the power of A.

6. For the work done by gravity, we only need to consider the work done by gravity in the vertical direction, and the speed and displacement in the horizontal direction have nothing to do with it, the work of gravity is equal to the change of gravitational potential energy, if the ground is the zero point of potential energy, the change of gravitational potential energy should be mgh-0=150*, and the power is w t=;

7. The mass of the two is equal, the departure time is the same, the result A to the 8th floor, B to the 7th floor, then it means w A" w B, P A "p B", at this time the speed A is greater than B, the displacement A is also greater than B, we consider the force in the vertical direction, it should be mg, the same force if the mass of two people is the same, the power of the speed is large, and the displacement is large.

Summary. For the simplification of fractional radicals, the radicals in the denominator are generally eliminated by the square difference formula, so that they can be simplified very easily.

7-4 3) (5-3 3)

Dear, this question will take about two minutes, and I'll send it to you right away!

The calculation process is as follows: (7-4 3) (5-3 3) = (7-4 3) (5+3 3) (5-3 3) (5+3 3) = (38 + 21 3-20 3-36) (25-27) = (2- 3) (2) Slow = 3 2-1

For the simplification of fractional radicals, the radicals in the denominator are generally eliminated by the square difference formula, so that they can be simplified very easily.

For this brigade attack, the calculation process is as follows: (7-4 3) (5-3 3) = (7-4 3) (5+3 3) (5-3 Sen Brother 3) (5+3 3) = (35+21 3-20 Zhencha 3-36) (25-27) = (1- 3) (2) = 3 2+1 2

Dear, look at the following formula, 3 2+1 2 is correct.

Thank you. 13. How to do the second sub-question.

That's the right answer.

It's equal to minus 210, that's right

[The shape, size, and material are exactly the same, so f1 = f2 = mg, and p1 is obtained from p = f s [there are small pits, increasing the pressure; The soft rubber sleeve increases the contact area and reduces the pressure

The density does not change, and the mg becomes smaller, that is, f becomes smaller, so the pressure becomes smaller

5a 6, equal to uniform linear motion n acceleration 5n 8, small increase pressure.

6.The work done by the pulling force is equal to the distance traveled in the direction of the pulling force (when the pulling force exists), w=fs=20 times 10=200, and the object does not have a displacement in the direction of gravity, so the work is 0

7.In the process of downward pressure, the gravitational potential energy is converted into elastic potential energy, so it decreases and increases due to the delay in filling the town.