Physics Topics!!! It s going to be dead!!

The two go in opposite directions, and the distance traveled by the car plus the distance traveled by the train is the train length.

That is, the car is driving at a constant speed of 36km h on the highway parallel to the railway, the speed is 10m s, and the driving distance is 10m s*7s=70m.

That is, the speed of the train is 54km h, that is, the speed is 15m s, and the driving distance is 15m s*7s=105m, so the train length is 70+105=175m.

Suppose the car is stationary, and the train passes the car at a speed of 100 kilometers per hour in seven seconds, so do the math of 100 meters per hour multiplied by seven seconds.

This is too simple, right, big brother, study hard.

36+54 90 90 m sec.

25*7 175 meters.

7 * 36000 3600 + 7 * 54000 3600 = 175 meters.

That is, the car is driving at a constant speed of 36km h on the highway parallel to the railway, the speed is 10m s, and the driving distance is 10m s*7s=70m.

That is, the speed of the train is 54km h, that is, the speed is 15m s, and the driving distance is 15m s*7s=105m, so the train length is 70+105=175m.

Cars and trains move in the same direction, regardless of the length of the car, we can think of the car as a point. In this way, 36km h = 10m s, 54km h = 15m s. So, the full length of the train.

10m/s+15m/s）×7s

175m

The speed of the car + train is multiplied by the time and the length of the car.

This is a formula.

(m+m)g-p0*s

p0*s upstairs didn't notice f=p0*s, the method is the same, but it's more correct.

The ground support force for the cylinder is (m+m)g-f;

The static friction between the piston and the cylinder wall is.

mg+ps-p0s-f|

p is the air pressure outside the cylinder.

The cylinder is first analyzed for force.

The vertical direction is supported by gravity and triangular prism inclined plane vertical component, the horizontal direction is supported by wall thrust and the horizontal component of triangular prism inclined plane support force, where the vertical direction force is determined.

The vertical component of the force supported by the triangular prism bevel = gravity.

Combined with the angle of the bevel, the law of parallelograms.

The triangular prism bevel support force and its horizontal components can be calculated.

The triangular prism is then analyzed for force.

The vertical direction is subject to gravity, and the vertical component of cylindrical pressure.

The horizontal direction is affected by the ground friction force and the horizontal component of the cylindrical pressure, wherein, the vertical component of the cylindrical pressure = the vertical component of the triangular prism inclined plane support force = the horizontal component of the cylindrical gravity cylindrical pressure = the horizontal component of the triangular prism inclined plane support force (action force, reaction force) Then it is easy to do, the simultaneous equation, compare the relationship between the horizontal component of the cylindrical pressure and the maximum friction force on the ground.

Among them, if sliding friction occurs, and the ground friction = friction coefficient (cylindrical gravity + triangular prism gravity) is not uploaded**, I can only talk to you about qualitative analysis.

But it should have been made clear.

(1) Sunlight is reflected on the wall when it hits a flat mirror.

2) 20 degrees by specular reflection properties, compared with the original reflected light 20 degrees (3) A figure pinch?

4) 10 degrees 20 degrees.

The plane mirror is turned back 10 degrees and at an angle of 10 degrees to the person (the person is considered vertical when standing), and the angle between the image and the mirror is of course the same angle.

At this time, the image is 20 degrees from the vertical line, and the previous image was also vertical.

5) When the mirror rotates 90 degrees, when the mirror is perpendicular to the object, the image is a reflection B pinch?

Ideally.

500cm3 saline, mass 600 grams, density p=m v= g cm = due to the density of pure water 1 10 kg m, the density is required, so it does not meet the requirements, to add water x kg, get x =

=m v=Because of <, it doesn't fit.

That's all it can be, the rest, I can't remember it's been a long time since I touched it, you can ask the teacher.

It should be 2500r per kWh, then if you turn 500r, you will consume 1 5 = kWh =

2500r kWh means that the meter turns 2500 times to take one kilowatt-hour of electricity, 500r = 3600000 5 = 720000j of electric energy.

It's not easy, dividing 500 by 2500 gives you the answer.

The mistake of choosing ba is that when the force is just withdrawn, the kinetic energy and potential energy are both increased, the error of cd is the same, the buoyancy is greater than the gravity, so the resultant force is upward, do positive work, and the kinetic energy of the velocity increases, when the buoyancy is equal to gravity, the velocity is the largest, the kinetic energy is the largest, and then the resultant force is downward, the kinetic energy is reduced, and at this time part of the wooden block is still in the water, neither the upper surface nor the lower surface.

It's not the fastest, but the fastest one is wrong, misleading.

I choose BThe position goes up, and the potential energy increases; As the velocity increases, its kinetic energy increases.