Physics solves how the mechanical energy of the EMU changes uphill at a constant speed

The kinetic energy of this process does not change, and the gravitational potential energy increases. The total mechanical energy is increased.

Uniform motion is a two-force balance. From the kinetic energy theorem, the total work done by the resultant external force on the object is equal to the increase in the kinetic energy of the object.

Here the two forces are balanced, the work done by the combined external force is zero, and the kinetic energy does not increase. [This conclusion is correct, don't doubt it] Don't think that if this kinetic energy does not increase, the total energy does not increase.

The condition for the conservation of mechanical energy is not that the resultant force on the object is 0, the condition for the conservation of mechanical energy is that only gravity does work on the object, you see that in the free fall motion, the net force on the object is not 0, and the mechanical energy is conserved. Hope!

It stands to reason that it should be increased, but at this time, the car moves at a constant speed, and the kinetic energy remains unchanged, but the potential energy is constantly increasing, so the mechanical energy is constantly increasing. As for the uniform motion, the car is indeed in equilibrium at this time, but it is not a two-force balance, but a four-force balance, that is, friction, support, gravity, and traction, and the sum of all the forces doing work is zero, but this can only ensure that the kinetic energy remains unchanged, and cannot reflect the change of gravitational potential energy. Traction (i.e., the force provided by the engine, which provides static friction through the pure rolling of the tire) does work, balances the frictional force, and overcomes the gravitational force to do the work, so at this time the gravitational potential energy increases, that is, the mechanical energy increases.

I'll help you solve it, it's the easiest.

Since it is said that the constant velocity does not consider the change in kinetic energy because the kinetic energy only changes with the change in velocity and mass. The kinetic energy does not change.

And when he says uphill, it means to go to a high place, and the gravitational potential energy should be considered, because the gravitational potential energy only changes with the change of height and mass. Yes, because it increases, the gravitational potential energy increases.

Whereas, mechanical energy is the sum of gravitational potential energy and kinetic energy, since the kinetic energy does not change, the gravitational potential energy increases. Needless to say, the mechanical energy will definitely increase.

Will not continue to ask.

It is true that the net force is zero and the linear motion at rest and uniform velocity, but the conversion of other energies is not considered here, but only the transformation between gravitational potential energy and kinetic energy. That's how the question is answered. Don't talk nonsense upstairs and downstairs, you have to be able to read, little brother.

Constant motion, kinetic energy unchanged; Uphill, the potential energy increases.

So the mechanical energy increases.

Classmates, don't forget the energy conversion The motor car consumes electrical energy, and its kinetic energy remains the same, but the gravitational potential energy increases, that is, the electrical energy is converted into mechanical energy. This is the law of conservation of energy.

When the car goes uphill at a constant speed, the mass remains the same, the speed does not change, and the kinetic energy does not change; The mass remains the same, the height increases, and the gravitational potential energy increases. Increased mechanical energy

Therefore, choose B

When the car goes uphill at a constant speed, the mass remains the same, the speed does not change, and the kinetic energy does not change; The mass remains the same, the height increases, and the gravitational potential energy increases. Increased mechanical energy

Therefore, C

In the process of the car going downhill at a constant speed, its mass remains the same, the speed does not change, so the kinetic energy does not change, the height decreases, the gravitational potential energy decreases, so the mechanical energy decreases

Therefore, C