A high school physical mechanics problem, a high school physical mechanics problem

AB is relatively stationary and can be analyzed as a whole.

At time T0, the overall force is 0 and the acceleration is 0, so the static friction between AB is zero, and A is wrong.

During the time of 0 - t0, the object accelerates, and the speed is the highest at the time of t0, b pair.

At 2t0, the overall deceleration is reduced to 0, but the acceleration is the largest, so the c pair.

The object accelerates first and then decelerates, but the direction of velocity does not change, so D pairs.

Answer: The overall acceleration of object A and B decreases uniformly in the forward direction with time, which is 0 at t0, increases uniformly in reverse, and is maximum in reverse at 2t0. Then the whole first does the acceleration motion with smaller and smaller acceleration, and then does the deceleration motion with the acceleration increasing, then the velocity is the largest at t0, and the whole has been moving forward in the time from 0 to 2t0, and the velocity is exactly zero at 2t0, so b and d are correct; For object a, it is known from Newton's second law that the acceleration is generated by the frictional force in the horizontal direction, and the acceleration is the largest at t0, and the acceleration at t0 is zero, so the friction force at t0 is zero, so the term a is wrong.

A False The static friction of ab at time t0 is 0

b is 0 for t0

c to the static friction of the isolation method is f

d for which velocity is 0

The conditions are insufficient to judge.

Add a point for upstairs: in the time of 0-t0, because the direction of force f is always consistent with the direction of the velocity of the object, the object accelerates, the force f is zero at time t0, and the velocity is the maximum at time t0, and the direction of force f is opposite after time t0, and the object begins to decelerate, so b is the correct answer.

This topic is not interesting if it is to be calculated in detail. Actually, it's a test of your understanding of the coefficient of friction and inertia. The coefficient of friction cannot be greater than 1, which means that in both cases of 2 and 3, the object will definitely slide.

The difference between option d and the other options is that in option d, the object gets its maximum velocity because it is a continuous acceleration process, although the acceleration becomes smaller. In this way, whether it is in the acceleration process ) or the deceleration process (1), d can go the farthest.

Because when the tensile force is zero, it is stationary (first action) or deceleration motion (under the premise of initial velocity), so if the displacement is the largest, the initial velocity should be maximized, and the initial velocity is the largest under the action of mg and 2mg, so the displacement is the largest when 3, 2, 1, or 2, 3, 1, because there is only 3, 2, 1 in the problem, so D is selected

The formula used: x=v0t 1 2at 2, x is the displacement, v0 is the initial velocity, and a is the acceleration (a=f m, f refers to the resultant force).

v=v0＋at