How do I do these two physics questions?

1 I'll put this question in my space, and you can see the following page:

2 Let the upward speed of the elevator be v m s

According to the title, it can be obtained:

42 (vA+v)=45 (vB+v) "Think of the number of stairs as the distance".

3v = 42v B - 45v A "here should be relative speed".

v=(42* "So, the speed should be v person + v elevator".

v= < v=s t time is constant

is a multiplier sign) 2.The number of people in each level is the same as the number of steps in the elevator, and the number of steps in the same way is the distance in the unit time.

s=vt s=s).

This should be the number of steps.

But the elevator is an ellipse, and it needs half the capacity to stand people.

Number of people = 204 2 = 102 (people).

Answer: 1) The total work done by the device w=fs=250

If the object rises at a constant speed, the object overcomes gravity and does work.

w'=mgh=200

Mechanical efficiency = w' w = 80%.

2) Knowing from the meaning of the title.

The resistance f'=, let the tensile force be f

The mechanical efficiency of the block pulley is 80, so 2FX80 = F'

So f=1500n

The speed at which the car is moving forward is v=

So the speed at which the person pulls the cart forward is v'=2v=

Power p=fv'=300w

What is the mechanical efficiency of the device if the object weighing 100n is pulled from the bottom end of the inclined plane to the top at a uniform speed by using the device shown in Figure (1), and the length of the inclined plane is 5m, the height is 2m, and the tensile force f=50N?

w useful gh 100n*2 200j

Total fs 50N*5*2 500J

The mechanical efficiency is equal to wuseful wTotal 200 500 40%2A car accidentally drove into the quagmire, the driver took a set of pulleys to pull the car out of the quagmire, as shown in Figure (2) if the car weight is 8 10000N, the resistance of the car is times the weight of the car, and the mechanical efficiency of the pulley block is 80, Q: (1) How much force does the driver need to use at least to pull the car out of the quagmire?

2) If the speed of the car is when the car is pulled, what is the power of the driver's work?

Resistance 80000*

Mechanical efficiency resistance (tensile force*n).

80% = 2400n (F-La*3).

F-La 1000N

Power: F*V: 1000*W.

The length of the inclined plane is 5m, and the height is 2m"It can be seen that sina is a for the slope angle).

Don't look at the pulley first, pulling the object up the inclined plane requires f=g·sina = 100*, so the mechanical efficiency of the device is 40 50=80%.

1.It is known that the length of the inclined plane is 5m, the height is 2m, and W has = GH = 200 JW total = FS = 250 J

Mechanical efficiency = w has w total =

Resistance = number of segments of the pulley block n = 2

f=fresistance n=1200n

V car = V rope = NV car =

P=FV rope=360W

Question 2 is incorrect.

It should be 1 meter per second and 70 people, I have done this mentions, by the way, I have also done the last question.

At first, I typed out the solution process, but it disappeared, so I was too lazy to think about it, and set up the unknowns, and the unknowns could be eliminated.

Question 1: 450 (20+30) = 9 seconds, this is the concept of relative velocity. The person sitting in the train thinks that his speed is 0, then the speed of the wagon is the superposition of the actual speed of the train and the wagon (with reference to the people on the ground).

Question 2: Choose A, in the same time, Xiao Ming always runs 10 meters more than Xiao Hong, that is, when Xiao Hong runs 90 meters, Xiao Ming has already run 100 meters. Now Xiao Ming started 10 meters back, in fact, when there were still 10 meters to the finish line, Xiao Ming had already caught up with Xiao Hong (Xiao Ming ran 100 meters, Xiao Hong ran 90 meters).

Because Xiao Ming's speed is faster than Xiao Hong, Xiao Ming finally reaches the finish line first.

When Xiao Ming runs 100 meters, Xiao Hong can run 90 meters, so Xiao Hong always arrives 10 meters behind, right?

So now Xiao Ming is 10 meters back than Xiao Hong (Xiao Ming is 110 meters from the finish line, Xiao Hong is 100 meters from the finish line), and the two start running. When Xiao Ming ran 100 meters, Xiao Hong ran 90 meters, and the two were side by side when they were 10 meters away from the finish line, and then there were 10 meters to run.

When Xiao Ming finished the last 10 meters, Xiao Hong only ran 9 meters, so in the end, Xiao Ming was 1 meter ahead of Xiao Hong to reach the finish line, understand?

The second question is like this.

I'll think about the first question.

<> amount of Cl- in AGCL: = 3molBaCl2 2NaCl

The amount of HCl substance: 3-4 =

cl2 ~ na2so3 ~ 2hcl

1mol 1mol 2mol

x yx = y =

4HCl 2HCl (oxidized) Cl22mol 1mol

zz = v(hcl) = 132ml

The mixture contains Cl2: =

The mixture contains SO2: =

The total amount of Na2SO3 substance: += 1molC(Na2SO3) = 1mol=

A: The volume of hydrochloric acid to be oxidized is 132ml, and the concentration of the substance in the original Na2SO3 solution is 2mol l.

Big brother, this is really .........Thing .........Questions? I'm bitter .........

It's really hard to do!

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(

Hello classmates, force analysis to do it yourself,

Subject: This is the first question. If you haven't studied calculus, the first one can be ignored.

: A little girl growing up in the trajectory of our life is constantly improving our own interests, developing relationships, and you can all be prepared.

Conditions for a solar eclipse to occur on Earth: The Moon must be between the Earth and the Sun.

And the conditions for a certain area of the earth to see a solar eclipse are:

The Moon is located between the Sun and the Earth, and this area faces the Sun and is located on the line of the three.

First of all: taking the earth as a reference: the period of the moon's rotation around the earth is: 1+1 30=31 30 d

Then: the relative angular velocity is: m=2 *30 31=60 31 rad d The period of rotation of the Sun around the Earth is:

1+1 365=366 365 d: The angular velocity of the Sun relative to the Earth is: r=2 *365 366=730 366 rad d

When a solar eclipse occurs, the conditions for the most recent reoccurrence of a solar eclipse are:

The difference between the angle of the Sun and the Earth minus the angle of the Moon in relation to the Earth is 2, then there is: n( r- m)=2

n=2π /（ωr-ωm）=2π /（730π/366-60π/31）=2/ d

That is, the period is: days.

Hope it helps.

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

1. The mass of the spilled water is, the volume is, and the density of the metal is divided by so this metal may be copper.

2. (760+1140) divided by 500=hours.

Hours = 3h48min

3h48min-2h42min=1h6min=500 multiplied.

(1) The ampere force of the current in the magnetic field is substituted by the ampere force formula f bilsin into the formula f=1

2) First of all, let's talk about a knowledge point: when the area is parallel to the direction of the magnetic field, the force f is f bis (s is the area parallel to the magnetic field, s=s*cos This angle is the angle between the plane and the magnetic field, but it should be noted that this question is the angle between the normal and the magnetic field).

First, find the area parallel to the magnetic field, s=s*cos(90-60), and then substitute f bis to find the output force.

Note: The unit of area is the conversion of the unit of square meter.

Sorry, the last question is to find the magnetic flux, I read it wrong.

bs, the applicable conditions are b and s