A simple physics problem with prawns to come

In order to increase the pressure and thus the friction.

Because each additional point of area is also under pressure, the pressure increases and the friction increases, i.e., the friction at the same point of contact remains the same, but there are more of these points. So the friction has become greater overall.

Isn't it simple.

Friction is independent of the contact area.

That's it. Ladies and gentlemen, see the question "negative explanation".

It's a college physics and mechanics topic that involves calculus, and I don't know what grade you're in right now. Really interested in knowing or ran into a problem to solve.

And I'm telling you for sure, calculus is going to be used to solve this problem.

This is because the force is not exactly the same at different points. As for why your teacher replied to this question, it is estimated that he ignores those effects, thinking that every point is the same. It's sturdy and convenient, but if you want to figure out how much force it is, you have to ......Hehe.

The increase in the contact area is not the reason, but the positive pressure is the cause.

Therefore, the fact that friction is independent of the contact area refers to the situation that other conditions are unchanged, such as a brick with the same gravity in the horizontal plane, regardless of whether it is placed on the side or vertically, the friction remains unchanged.

Friction is only related to positive pressure and coefficient of friction (roughness of the contact surface), and positive pressure is not gravity.

I think it is not only related to friction, but also related to pulleys, because the number of strands of the rope is more, and the force on each section is smaller, so it is not easy to break.

A few more turns increase the contact area, but the friction is not related to the contact area, so the friction remains the same.

And the strength of the ox is the same, so it will run away, and it has nothing to do with a few more circles.

The pull of the ox is too great, the friction of the rope is too small, and it will definitely run away.

If you make a few more turns, the contact area between the rope and the tree will increase, the friction will increase, and it will be difficult for the ox to run away.

Doing so increases the contact area between the rope and the tree, which increases the static friction.

The mass of kerosene is 120-80 = 40g =

Density = mass volume, pay attention to the unit, the density of the object does not change with the number of objects.

The density of kerosene is.

The mass of the remaining kerosene is (3 4) * 40 = 30 g and the density is.

1) =m2-m1 v=120g-80g 50cm 3=2) Because 1 4 kerosene is used, so m'=（1-1/4）(m2-m1)=3/4*40g=30g

The density is unchanged. 1）2）30g

The mass of 50cm kerosene is (120-80)=40g, then the density = (mass volume) = 40 50=

After using 1 4, then 3 4 remains, then the remaining mass is 40 3 4 = 30g; The density remains the same, still.

Density of kerosene = mass of kerosene Volume of kerosene = 120g-80g 50cm3=

30g③

Kerosene 120-80 = 40 g =, density.

Use 1 4 to leave 30g, the density remains the same, but the unit changes,

1.Deceleration in the second second then we can know that the acceleration is 64 by using the formula s=v*v 2a to find the displacement

2.A binary system of equations can solve the problem, and the reaction time is t, and the first braking time is t1, and the second is t2.

v1*t+v1*v1/2a=s1

v2*t+v2*v2/2a=s2

The solution yields t=3The acceleration and deceleration time is 3 seconds, then it can be judged that the displacement at both ends is equal, and the acceleration is calculated as 1m s

Then the displacement of the acceleration phase is a*t*t 2= and the corresponding deceleration phase is also the displacement of the constant phase is vt=18

The total displacement is. 4.Find the acceleration first using the formula.

v*v-v*v) 2a=s Here v can be regarded as the velocity of point b, v as the velocity of point a, and here we get the acceleration a

V+AT=V The process from point A to point B.

After calculation, t=4s

5.A simpler method can be used to find the velocity through the middle of the window and the average velocity through the window process.

v=s/t=10m/s

It can be known that the time from the moment when the object falls to the moment when it passes through the middle of the window is v g=10 10=1s, pay attention; If the time to the middle moment is 1s, the time to fall to the top of the window.

Then the distance should be h=g*t*t 2=

I'm so tired of typing so many letters.

1. Solution: Because the speed of the brick in the 2nd s decreases all a=, the brick can slide 8m= on the ice surface

Between 0 and 1s, you set f=maThen look at the slope, a=1 is the one with the highest velocity. And then you're looking at the slope from 3s to 5s, which is 2 v=a2, and the deformation gives a2=2a

Then f=ma is brought in. f2=2ma, f2 2=ma, so at this point f2=1 2f. But pay attention to the direction, which is the opposite.

With the resultant external force you can find the following, the velocity from 1s to 3s The variable is 0, f=ma, you can know that the resultant external force is 0, no work is done, between 3 and 5 seconds, the resultant external force is -1 2f, the displacement is the area of that part of the image, that is, 2s, w=fs can know w= -1 2f 2sIn combination with w=fs know = wBetween 5s and 7s, the acceleration does not change, but the displacement changes in the opposite direction.

So the displacement is -2s. With the formula, the work done by the external force is w. The displacement between the 3s and the 4s, yes, can be found.

In the band formula w=fs=.

Bonus thanks.

What is Acceleration? Acceleration is the rate of change of velocity to time, then, the slope in v-t is also the acceleration, and according to the slope, find the acceleration a for each period, and f=ma can be deduced.

The key here is to use w. Because it can be seen from the diagram that there is acceleration in 0 to 1 second, and if there is acceleration, then the resultant external force is not zero. f=ma。That's how the power comes from. As for m, you can keep it, and you will definitely be able to get rid of it in the end.

According to the kinetic energy theorem, an object is moving on a smooth horizontal plane, so the amount of kinetic energy change of the object in the same period of time is equal to the amount of work done by the resultant external force.

When the mass is constant, according to the ratio of the slope is equal to the ratio of the external force (note the direction), the ratio of the displacement is equal to the ratio of the area.

Using the kinetic energy theorem, the work done by the combined external force is equal to the amount of change in kinetic energy.

If a drop of muddy water splashes on the upper part of the camera lens, it is equivalent to blocking a part of the light, and the part that is not blocked can also be imaged, but the brightness is slightly dimer; Therefore, you can also see the full-body portrait of the classmates taken, but the scum silver hole will be darker

Therefore, choose D

d You can see the full-body portrait of the classmate taken, and the image of the fighter will be darker.

This drop of muddy water does not affect the imaging. It only weakens the light passing through the lens.

Please give praise to the banquet in a timely manner, and ask questions if you have any questions. I will always help you. Good luck!

1. (1) According to g h fl = efficiency 6g 22l =

5g/fl=

The above two equations yield: f=200n

The second question: g=300 f=200, then l=10m, p=f*l, t=200*10, 10=200w

2 I can't see where S1 is connected.

According to the principle of kinematics, in the process of motion to the right, the friction force between the wooden block a and the skateboard b makes the skateboard b also move to the right, because there is a velocity difference between the two at first, so the wooden block a will finally compress the spring, the velocity of the wooden block a in this process continues to decrease, and the speed of the skateboard b continues to increase, until the speed of the two is equal, because there is no speed difference, so the wooden block a also no longer compresses the spring, at this moment, the compression amount of the spring is the largest, that is, the spring is compressed to the shortest. The velocity at this time can be solved by the equation of conservation of energy and the simultaneous conservation of momentum.

If there is no same velocity, there will inevitably be a relative displacement between the two, and the distance between the two will inevitably change, that is to say, the length of the spring must change, and the spring is not the shortest, so only when the two have the same velocity, relatively stationary, the spring is the shortest.