How to do these two questions in junior high school physics?

1.The distance traveled by the car is S1, the distance traveled by the person is S2=9m, the speed of the car v1=216km h=60m s, and the speed of the person v2=

That is, s1 = v1 * s2 v2 = 60m s * 9m so it is safe for him to cross the railway at least 360 meters away from the car.

2.The first question is correct, and the second question is to find the total time spent, and then find the velocity, which is the average speed of the whole process.

The time taken in the second half of the journey is t=250m 5ms=50s, the total time taken is t=250s+50s=300s, and the average speed of the whole process is v=s t=500m 300s=

Satisfaction Hope.

It takes 9 to cross

The train travels in 6 seconds s=216km h*6s=60m s*6s=360mThe time taken in the first half of the journey t1=s v1=500*1 2 1=250sThe time taken in the second half of the journey t2=s v2=500*1 2 5=50sThe average speed of the whole process v=s (t1+t2)=500 (250+50)=5 3=

(1) The heat released by the complete combustion of gasoline: q discharge = qm =, the power consumed by gasoline p1 = q t =

2) 72km h=20m s, 10min=600s, the distance that the car passes within 10min s=vt=20*600=12000m

The work done by the traction of the car within 10min w=fs=

The power of the car traction is made p2=w t=

3) It was found that the power of the car's traction work was less than the power consumed The reasons include: gasoline is not completely burned; Exhaust gases take away part of the heat; Loss of a part of the energy due to heat transfer; Overcoming friction consumes a part of the energy, etc.).

1) Power consumption p1 = mq t = [Note: (7) represents the 7th power, please change it by yourself].

2) Traction power p=fs t=fv=

3) Only a small part of the heat burned by gasoline is used to tow the car to do work, and most of the power consumption is lost.

Reasons:1Power loss between the mechanical transmission of the car2Friction between the car and the road surface is lost in heat.

（1）（2）p=

3) A car exhaust gas takes away a lot of energy, b the car overcomes frictional resistance and consumes a lot of energy.

p = r²v × v² /2= πr²v³ /2

In ...The measures that can be taken to accommodate the negotiation are:Increase the length of the blades of the wind turbine. Bi Li

p=ui, i.e., 6=12ii=

The voltage obtained by the resistor: U=36-12=24V

Because the series resistance and the current of the bulb are equal to.

So the resistance of the resistor r=24 ohms.

The electrical power consumed by the resistor: p=ui=48*

According to the P UI, the rated current I P U 6 12 can be known, so the total resistance R is always 36, and the R lamp is 12, and the resistance of 48 should be connected in series, and the electric power consumption is 12W

According to the formula of electrical power, p=ui brings 12v and 6w in, so 6w=12v multiplied by i to calculate i=2a

Bringing out 36V 2a according to i=r/u yields 18 ohms.

Normal luminescence, the resistance on the lamp should be 12V, then a series of resistors must be connected to divide the voltage of 36-12=24V. Normal operation i=p u=6 12=, the series current is equal, then r=u i=24. The electrical power consumed is p=i u=.

1. The total volume v=m p=89kg (

1mm^2=(1mm)^2=(1*10^-2dm)^2=1*10^-4dm^2

Cross-sectional area s=25mm2=25*10 -4dm 2Lengthl=vS=10dm (25*10 -4dm2)=4*10 3dm=400m

It is known from density = mass divided by volume, volume = mass divided by density = 89kg to the power of 3 = 1 10 negative quadratic m

From volume = base area height (that is, length) to know height = volume base area = negative power of 1 10 25 minus 9 power of 10 = sixth power m

v=m =89 8900=m³ l=v s=. The answer can't be 400m.

m=ρ×s×l。where m is the mass, is the density, s is the cross-sectional area, and l is the length. Do the math yourself. Note that the cross-sectional area should be converted to m first. The square should be 10 -6.

You first distinguish whether it is copper or steel