Junior 3 Physics, Junior 3 Physics,

The speed ratio of the escalator is 3:1

Therefore, the ratio of the speed of the person to the speed of the person + the escalator is 3:4

It takes a minute for a person to walk up a stationary escalator, so it takes a minute to walk on a moving escalator.

Set the elevator length to S

The distance from the ground floor to the top floor is s=v1*60, and the distance from the ground floor to the top floor is s=v2*180 when a person stands on the escalator, and the distance is equal to the distance s by speed and multiplied by time, that is: (v1+v2)*t=s, calculate the time t, which is how much time it takes for a person to go upstairs along the moving escalator.

Answer = 45 seconds.

Minute. The speed of the escalator is x m min and the speed of a person is y m min. There are z meters from the ground floor to the top floor, and it takes a minute for people to go upstairs along the moving escalator.

Then x=z, 3y=z, (x+y)a=z

Substituting , substituting to get (z+z 3)a=z, and the solution gets a=

Solution: Let the total distance be x, the speed of the person is v1, and the speed of the elevator is v2, then.

s/v2=1………1）v2=3v1

s/v1=3………2）

1) (2) Lianli Disk v2=3v1 ,s = 3v1 so the time to take the elevator upstairs is s (v1+v2)=3v1 (v1+3v1)=3 4

min）

Solution: When it reaches position 1, R2 and R3 are short-circuited, and by P=U2 R, when the voltage is constant, the greater the resistance, the smaller the electrical power, and the resistance is the smallest when the switch is connected to 1, so the heating power is the largest, and the heating power is 90W

At this time, R1 U 2 P1 (36V) 2 90W=refers to position 2, and the heating power P is 72W from 1 analysis, so the circuit current I p U=72W 36V=2A

The voltage at both ends of R1 is U1=IR1=2A

Therefore, the voltage at both ends of R2 is U2=U-U1=

When it is pointed to position 3, the heating power p = 45w is analyzed by 1, so the circuit current i = p u = 45w 36v =

The question is a bit cumbersome to calculate, and the score of 20 is a bit low.

As can be seen from the figure, S is at 1 and there is only one resistor R1, that is, the power is 90Wp1=U R1 can be calculated as Ri=

S in series at 2, R1, R2, power 72W

P2=U (R1+R2) R1+R2=18 R2=S in 3, series, power 45W

p3=u²/(r1+r2+r3) r1+r2+r3= r3=

The resistance values are clear.

2: When S points to position 2, what is the voltage across R2?

Current i=U (R1+R2)=Voltage at both ends U2=IR2=3When S points to position 3, what is the current in the circuit?

i1=u/r1+r2+r3=

Hehe, it's over, it's quite detailed, the touch sensor is the role of the switch, don't care.

This question is a test of the calculated deformation of electrical power. Actually, it's not that hard.

At the moment when the resistance decreases or increases, the current through the branch increases or decreases, while the current of the other branches does not change, so that the main circuit current changes, the voltage does not change, and the total resistance decreases or increases according to Ohm's law.

Copper = volume of the statue v = m wax p wax.

The mass of the copper required m copper = p copper * v =

2.The volume of the bottle v = m water p water = 1000 ml mercury density p mercury =

m mercury = p mercury * v mercury = 13600g =

1. The third step is: fill the empty beverage bottle with milk, measure the total gravity as g3, and find the mass of the milk as m=(g3-g1) g, and the density p=m v=[(g3-g1) g] [g2-g1) g]=(g3-g1) (g2-g1).

2. Density p=(g3-g1) (g2-g1)3,After measuring the density of milk as cubic cm, and knowing that the density of milk is cubic cm, you can determine whether it is mixed with water by comparing the two densities.

Please click here, you can ask if you don't know.

The square at the beginning of 90mv - the square at the end of v = 2as (a is the acceleration) solution a =

After another 50 seconds, v2=

Because V2 is less than 0, the speed of the car is already 0 after 50s, so the square at the end of V = 2as

The dry band is solved s=90m

You won't ask me again without a reed, ok?

First, find the acceleration a=(64-36) and 140=

Then find the time used to reduce the speed to 0 t=6 <50, so when the car has stopped at 30 seconds, you can find the distance of the forward circle only s=

1.Take any one of the bulbs from the dust of the world, and if the other no longer glows, connect them in series; If still glowing, in parallel.

2.I won't draw the picture. After the two bulbs are connected in parallel, they are connected with the electric bell in series, and the two switches are connected in series with the two lights respectively.

The battery pack ——— the green light ——— the electric bell ——— a switch - Lu Qi ——— the battery pack.

— The red light ——— another switch is guessed as ——— as a megalome.

That's what it means, and we'll see.

When the two lamp strips are lit, remove one bulb to see if the remaining bulb is bright or dark (string) Before the light line (and) Note: The bulb cannot be removed It can break a sleepy One is also effective.

1, kinetic energy = mv, object velocity should be considered. A false. B false.

The height of this position has nothing to do with the distance of displacement when doing work, at least it is not said in the question (work is related to displacement, w=f*s), so c is wrong. Gravitational potential energy = mgh, the same height is the same h, so d is right. I choose D

2. Even downhill means that the speed is kept constant, which is very important. The velocity must be a wrong, h decreases b pair, here mechanical energy = kinetic energy + gravitational potential energy, h decreases, gravitational potential energy decreases, kinetic energy = mv, v does not change, kinetic energy does not change, so the mechanical energy decreases, c is right, d is wrong. So choose BC

3, a is a constant velocity, so the kinetic energy remains unchanged, the gravitational potential energy of the lower bridge decreases, and there is no kinetic energy conversion potential energy. B is the same as A. c is a constant velocity, and the kinetic energy is constant.

d is the velocity decreases, the altitude increases, the kinetic energy decreases, the gravitational potential energy increases, the mechanical energy does not change (air resistance is not considered), and the kinetic energy is converted into gravitational potential energy. So choose D

1. Both da and b are wrong, kinetic energy is related to two quantities, mass and velocity.

C's fault lies in the fact that he did not determine the final position of the object, so the work done cannot be determined.

2. BC, downhill, the gravitational potential energy must decrease, and the kinetic energy does not change, so the mechanical energy decreases.

3. d, the velocity of the ball slowly decreases after it is raised, and it is converted into the potential energy of the ball.

Set the center of gravity from the front wheels is d1, from the rear wheels is d2When the front wheel is pressed on the scale, d2 g=2m f1. When the rear wheel is pressed on the scale, d1 g=2m f2.

The sum of the two equations gives 1 g=1 f1+1 f2 f1=3000n, and f2=2000n gives g=1200n

A bit esoteric, probably the principle of leverage.

v steel = m steel steel = 316

m C = v C C =

m reduction = m steel - m propylene = 316-48 = 268

The volume of the car v m p = 316kg times 10 to the 3rd power cubic meter = cubic meter After replacing steel with polypropylene plastic, m = PV = 3 power kg multiplied by 10 cubic meter cubic meter = 48kg

The weight that can be reduced is 316kg-48kg=268kg, please click to adopt, you can ask if you are not sure.

The hardness of 2-5 times in front of this question is a disturbance condition, you don't have to worry about it, it is to tell you that there is such a thing. After removing the first sentence, it is very simple, replace steel with plastic, there is a volume that has not changed, or the car is not deformed, v=m (steel) (steel).

m(plastic)=v* (plastic).

It should be noted that the question is how many kg can be reduced in the mass of the body

m = m (steel) - m (plastic).

The volume of the shell of the car obtained from p = m v is v = m1 p steel = 316 kg to the 3rd power cubic meter = ....

The mass of the shell of the polypropylene plastic car obtained from P=MV is M2=PVPro=....

The reduced mass of the body is m minus = m1 - m2 = ....

Do the math yourself.