There is a question about how to do a physics problem, please teach me Thank you

The analysis of the force of block A shows that the horizontal component of the elastic rope fx=x k increases; The vertical component fy=mg-y k is unchanged. （x：

The horizontal displacement of the block, which increases with the motion of a; y: the height of the nail to the ground, no change) and fy=fn, which can be seen from ff= fn, the friction force does not change. (Note:.)

This kind of physics topic is generally analyzed qualitatively, and then quantitatively considered in the case of no result. Although quantitative comparison is troublesome, it is a basic skill, and force analysis is very important. If you have done this problem, there should be no problem, and you should pay attention to the trigonometric relationship when solving the problem. Finally, I wish you physical ok

The friction is inferior.

The position of the nail in the natural length of the rope So the distance from point b to the object multiplied by the coefficient of elasticity is the force exerted by the rope on the object.

But its component in the vertical direction is constant, so the pressure of the object on the ground is constant, and the frictional force is constant.

The friction of a is at the time of ob to oa natural natural length ·· His friction does not change beyond the natural length of 0A to the maximum bearing limit of OA, and the frictional force gradually changes during the time when the object stops moving

Reason: When the natural length exceeds 0a, the rope produces elastic deformation, which will give the object a component force, and the upward force will reduce the friction ·· Value to the range of tolerance ·· Thank you...

a. The friction of the big dragon pond tiger's den changes.

The v in acceleration a changes at any time, so it is definitely not possible to calculate it directly, and it is necessary to use derivatives and integrals!!

According to: v 2 = 2 gh, v = 14 m s

Acceleration in water: a=dv dt=-kv 2 d--the meaning of derivation.

dv dt=dv ds*ds dt=v*dv ds=-kv 2: dv ds=-kv

s is the displacement of falling to a certain point, and v should be written as vs, i.e. velocity at point s) dv v=-kds

Make an indefinite integral and simplify: v=ce -ks

Introduce the initial condition, when s=0, v=v0=14, and when v=14e -kss point, v=14 10, and then substitute k to calculate s=

According to the formula final velocity squared = 2as - initial velocity squared, the water inlet velocity v= (2as)= 196 (a=g is taken and known as the water inlet acceleration a=-kv k=

Deceleration depth after entering the water s =(vt -vo ) 2a=(196-1) 2as =195 2(

Gauss's theorem: In an electrostatic field in a vacuum, the flux through an arbitrarily enclosed surface is equal to the algebraic sum of the charge charge enclosed within the surface divided by the vacuum permittivity.

So, choose D

(1)i=3/6=

2)=9-3=6v

3)r2=6/

String 10 ohm resistor.

1.(18-12) 12=x 20 gives x=10 then r=(18-12).

Do you understand?

(1) The current at both ends of the circuit series R1 is the current of the circuit, that is, I 3V 6 0 5A

2) The voltage at both ends of R2 is 9V, 3V, 6V

3) The resistance of R2 is 6V 0 5A 12

Method 1, if it can work normally, the current should be equal, and the voltage division of I 12V 20 0 6A resistor is 18V 12V 6V

Then the resistance is 6v 0 6a 10

In the second method, the resistor divider voltage is 6V, and according to their current equality, 12V 20 6V R then R 10

I'm more standardized, you give it to me, right??!

Because it is connected in series, i = 3v 6 ohms = u2 = 9v - 3v = 6v r2 = 6v ohms (1) 12v 20 ohms = 6v r r = 10 ohms (2) 12v 20 ohms = 18v r total r total = 30 ohms So r = 10 ohms This doesn't seem to be difficult at all.

1.(1) i=u1 r1=3v 6 = the current of the series circuit is equal (2) u2=u-u1=9v-3v=6v

3）r2=u2/i=6v/

2. (1) p=u^2/r=（12v）^2/20ω=r1=u2^2/p-r=(18v)^2/

The resistance of R1=6 and the resistance R2 are connected in series on the 9V power supply, and the voltage at both ends of R1 is 3V.

1.The current in the circuit (2The voltage at both ends of R2 (3.r2.

Solution: Because this is a series circuit, (1.)Current in the circuit = current at both ends of r1 = 3v divided by 6 = (2..)Voltage at both ends of R2 = 9V - Voltage at both ends of R1 3V = 6V

3.The resistance of R2 = 6V divided by = 12 A power with a resistance value of 20 is 12V at both ends of the electrical appliance during normal operation, if you want to use the electrical appliance to connect to the 18V power supply and still work normally, how big of a resistor is needed to connect it in series? (Please use two methods to calculate).

Solution 1: The resistive voltage in series = 18-12 = 6V and its current = 12 divided by 20 = a

So the resistance value = 6 divided by =10

Solution 2: The voltage in the series circuit is proportional to the resistance.

As: A resistor of x is to be connected in series.

Then 20: (20+x)= 12 : 18 gives x=10

1, (1), i=3 6=amps).

2), u2 = u—u1 = 9 - 3 = 6 (volts).

3),r2=u2 i=6 ohms).

2, Law 1: 12 20 = (18-12) r, r = 10 (Europe) Law 2: 12 20 = A), 18-12 = 6 (volts), 6 euros).

1,i=u1/r1=

2, because of the series, u2 = 9-3 = 6v

3, r2 = u2 i = 12 ohms.

Method 1: The resistance divider voltage is 18-12 = 6V, so r 20 = 6 12, r = 10 ohms.

Method 2: i=12 20= ,r=18 ohms.

（1）i=u1/r1=0.5a(2)u2= u-u1= 6v(3)r2= u2 i = 12 beats.

i=u/r=0.06a r=u total — u i 100 r1 r2 u1 u2 r2 100 beating....The phone called....

Solution: Let the radius of rotation of the ball be r, the distance from the horizontal plane is h, f1 is the support force of the bottom of the bowl to the ball, the component of fn along the vertical direction, and f1=g=mg; f0 is the centripetal force divided by fn, and other parameters and force analysis are shown in the figure below

The upstairs three is the process, and the answer is r-g w 2

Hello, according to Coulomb's law, first of all, it can be affirmed that it can only be located on the ab line Because each charge is subjected to the electrostatic force of the other two charges, and the sum is a dissimilar charge, the force they act on is one attraction and the other is the repulsive force, so it cannot be located between a and b; In addition, if it is to be in equilibrium, it should be far away, so it should be located on the left side of A, and it must be negatively charged

To sum up, the correct option for this question is A

This is a typical example question, and your question is good.

Translate v1 to b, with v1 as a diagonal and v2 as v2'is one side, take the collision B as the endpoint, make a parallelogram, get BC, translate BC to the collision A, and mark the arrow to get V1'

The drawing process and results are shown in the figure below (if the image is too small, click ** to enlarge it).