Педагогические науки/5.Современные методы преподавания

V. Novikov,

associate professor of HAC;

G.Kalakova,

a senior lecturer of computer science and mathematics of Kostanay State University named by A.Baitursynov;

B.Kalakov,

assistant professor of physics and GTD Kostanay State Pedagogical Institute

Pseudo solution of physical problems,

or why not obtained an answer to the problem

In studying physics, we solve a lot of tasks for consolidation of the material studied. There are also special lessons solution computation tasks. Often, by solving tasks teachers checked our theoretical knowledge of the material.

Not infrequently, the sums don’t lead to the correct answer. This is because the assumptions students’ commonplace mistakes: incorrect calculation, formulas misspelling, mistakes in the formula, not all values are recorded in a single system of units and etc.

However, mistakes happen, and the higher order, the main obtaining causes which, in our opinion, are the following:

- Not deep enough (comprehensively) analyzed the conditions of (to the task situation);

- in the analysis of the conditions task is not taken into account all the phenomena of magnitude, especially given in implicit form;

- - the substitution of physical concepts (values) is produced, use something that is not in the problem, or are looking for the wrong amount, you want to define;

- not all possible situations presented in a task verbally are examined at a decision;

- the borders of applicability of laws of physics are violated.

Such errors happen, mainly, at the decision of non-standard tasks that us offer teachers on optional employments, or at preparation to the Olympiads, on Olympiads (their different stages).

We will show it on the examples of certain tasks that we decided during the last three school years.

Task 1 Two plasticine balls are suspended on filaments so, that touching the centers of gravity are at a distance of 1meter below the point of suspension, and filaments are vertical. The masses of balls 10 and 40grams. Smaller ball is taken aside so that the filament is deflected from the vertical 900, and released. Determine at what height will be a large ball after absolutely inelastic collision.

Decision of student

In relation to position of equilibrium a smaller ball after the rejection of his filament on 900 possesses potential energy of mgh, where h = l (length of filament). This energy is then converted into its kinetic and in collisions with a large ball grows into kinetic energy of both balls, and eventually in their general potential energy of (M + m) gH, where H is the height of raising of balls.

But veritable answer: H = m²h/(M + m)².

The resulting student answer was incorrect because it was not taken into account the loss of mechanical (kinetic) energy (turning it into a deformation energy of balls - their internal energy) as a result of their perfectly inelastic collision.

After an inelastic collision balls will move with speed of u, determined by law of maintenance of impulse:

mv = (M +m)u, (1)

where v - speed smaller ball before the collision, which can be determined by the law of conservation of energy for the smaller ball:

mgh = mv²/2 (2)

From equalization (2) we will get: v = .

Putting this expression in(1), we will get for u:

u = . (3)

By the law of conservation and transformation of energy for a system of two balls have:

whence

H = u²/2g.

After a substitution(3) we will get:

H = m²h/ (M + m)².

The decisions of these two tasks also due to the shallow analysis described in these situations have been missed the conversion of mechanical energy into internal energy, which is why students were received incorrect answers.

Task 2 In the body of mass m₁ = 990 g, lying on a horizontal surface, gets a bullet mass m₂ = 10 g and gets stuck in it. Speed of a bullet v = 700 m / s is directed horizontally. Какой путь s пройдёт тело до остановки, если коэффициент трения между телом и поверхностью k = 0,05?

A veritable answer(g =9,8 m/ss) is a 50 m. students received - 5,000 m, or 5 km. Some students do not even embarrassed unreality obtained distance traveled, and those whom she was confused, looking for a mistake in the calculations, rather than the analysis of the physical situation.