1 . What kind of deformation experience under load:

a) bench leg;

b) bench seat;

c) stringed guitar;

g) screw grinder;

e) drill;

2 . What deformation (elastic or plastic) is dealt with when sculpting figures from clay, clay?

3 . The wire length of 5.40 m under the action of the load lengthened to 5.42 m. Determine the absolute elongation of the wire.

4 . With an absolute elongation of 3 cm, the spring length became equal to 27 cm. Determine its initial length if the spring:

a) stretched;

5 . The absolute elongation of a 40 cm long wire is 2.0 mm. Determine the relative elongation of the wire.

6 . The absolute and relative elongation of the rod is 1 mm and 0.1%, respectively. Determine the length of the undeformed bar?

7 . When the rod is deformed with a section of 4.0 cm 2, the elastic force is 20 kN. Determine the mechanical stress of the material.

8 . Determine the modulus of elasticity in a deformed rod with an area of ​​4.0 cm 2, if this results in a mechanical stress of 1.5 · 10 8 Pa.

9 . Find the mechanical stress that occurs in the steel cable at its relative elongation of 0.001.

10 . When an aluminum wire was stretched, a mechanical stress of 35 MPa appeared in it. Find the relative elongation.

11 . What is the coefficient of spring stiffness, which is lengthened by 10 cm with a force of elasticity of 5.0 H?

12 . How long is the spring with the hardness of 100 N / m extended, if the elastic force is equal to 20 N?

13 . Determine the maximum force that a steel wire can withstand, the cross-sectional area of ​​which is 5.0 mm 2.

14 . The tibial bone of a person withstands a compressive force of 50 kN. Considering the strength of a person’s bone to be 170 MPa, estimate the average cross-sectional area of ​​the tibia bone.

Level B

1 . Which bulb will withstand more pressure from the outside - round or flat-bottomed?

2 . What is the bicycle frame made of hollow tubes, and not solid rods?

3 . When stamping, parts are sometimes preheated (hot stamping). What do they do it for?

4 . Indicate the direction of elastic forces acting on the body at the specified points (Fig. 1).

Fig. one

5 . Why there are no tables for body stiffness kLike tables for substance density?

6 . At what laying of bricks (Fig. 2) will the lower of the bricks be under great stress?

7 . The force of elasticity is a force variable: it changes from point to point as it lengthens. And how does the acceleration caused by this force behave?

8 . A weight of 10 kg is suspended from a wire with a diameter of 2.0 mm fixed at one end. Find the stress in the wire.

9 . The same weights were attached to two vertical wires, the diameters of which differ by 3 times. Compare the stresses arising in them.

10 . In fig. 3 shows a graph of the stress arising in a concrete pile on its relative compression. Find the modulus of elasticity of concrete.

11 . A wire 10 m long with a cross-sectional area of ​​0.75 mm 2 under tension of 100 N was extended by 1.0 cm. Determine the Young's modulus for the wire material.

12 . What is the strength to stretch a fixed steel wire 1 m long with a cross-sectional area of ​​0.5 mm 2 in order to extend it by 3 mm?

13 . Determine the diameter of the steel wire with a length of 4.2 m, so that under the action of a longitudinal tensile force of 10 kN, its absolute elongation is equal to 0.6 cm?

14 . Determine on a graph (Fig. 4) the coefficient of stiffness of the body.

15 . According to the graph of the dependence of the change in the length of the rubber rope from the force applied to it, find the rigidity of the rope (Fig. 5).

16 . Build a graph of the elastic force arising in the deformed spring. F  cp = f(Δ l), from its elongation, if the spring stiffness is 200 N / m.

17 . Build a graph of the dependence of the elongation of the spring from the applied force Δ l = f(F), if the spring constant 400 N / m.

18 . Hooke's law for the projection of the elastic force of the spring has the form F x = –200 x. What is the projection of the force of elasticity, if the extension of the spring from the undeformed state is the projection of the movement of the end of the spring on the axis X  is 10 cm?

19 . Two boys stretch a rubber band, attaching dynamometers to its ends. When the harness lengthened by 2 cm, the dynamometers showed forces of 20 N each. What do dynamometers show when stretching a harness to 6 cm?

20 . Two springs of equal length, connected in series, stretch their free ends with their hands. The spring of 100 N / m has been lengthened by 5 cm. What is the rigidity of the second spring, if its elongation is 1 cm?

21 . The spring changed its length by 6 cm, when a weight of 4 kg was suspended to it. How much would she change her length under the influence of a weight of 6 kg?

22 . On two wires of the same stiffness, 1 and 2 m long, the same weights are suspended. Compare the absolute elongations of the wires.

23 . The diameter of the nylon fishing line is 0.12 mm, and the breaking load is 7.5 N. Find the tensile strength of this type of nylon.

24 . At what is the largest cross-sectional diameter of steel wire under the action of a force of 7850 N break?

25 . A 10 kg chandelier should be suspended on a wire with a cross section of not more than 5.0 mm 2. What material should the wire be taken from if it is necessary to provide a fivefold safety margin?

Level WITH

1.   If a wooden bar weighing 200 g is attached to a vertically arranged dynamometer, then the dynamometer reading will be as shown in Figure 1. Determine the acceleration with which the same bar begins to move, if it is pulled back so that the spring will extend another 2 cm and then bar to let go.

We have repeatedly used a dynamometer - a device for measuring forces. Let us now get acquainted with the law, which allows to measure the forces with a dynamometer and determine the uniformity of its scale.

It is known that under the action of forces arises body deformation  - change their shape and / or size. For example, from plasticine or clay, you can fashion an object, the shape and size of which will be maintained after we remove our hands. This deformation is called plastic. However, if our hands deform the spring, then when we remove them, two options are possible: the spring will completely restore its shape and size, or the spring will retain the residual deformation.

  If the body regains shape and / or dimensions that were before the deformation, then elastic deformation.   The force that arises in the body is   elastic force obeying   Hooke's law:

Since the elongation of the body is included in Hooke’s law modulo, this law will be valid not only for stretching, but also for compressing bodies.

Experiments show:   if the body elongation is small compared with its length, then the deformation is always elastic;  if the elongation of the body is large compared to its length, then the deformation, as a rule, will be plastic  or even destructive. However, some bodies, for example, elastic bands and springs, are elastically deformed even with significant changes in their length. The figure shows more than twice the elongation of the dynamometer spring.

To clarify the physical meaning of the stiffness coefficient, we express it from the formula of the law. We obtain the ratio of the modulus of elastic force to the modulus of elongation of the body. Recall: any ratio shows how many units of the value of the numerator per unit value of the denominator. therefore   stiffness coefficient shows the force arising in an elastically deformed body when its length changes by 1 m.

1. Dynamometer is ...
2. Thanks to Hooke's law, a dynamometer is observed ...
3. The phenomenon of deformation of bodies is called ...
4. Plastically deformed, we call the body, ...
5. Depending on the module and / or direction of force applied to the spring, ...
6. The deformation is called elastic and is considered obeying Hooke's law, ...
7. Hooke's law is scalar, since it can only be used to determine ...
8. Hooke's law is valid not only for stretching, but also for compressing bodies, ...
9. Observations and experiments on the deformation of various bodies show that ...
10. Since the time of the children's games, we know well that ...
11. Compared to the zero bar of the scale, that is, the undeformed initial state, on the right ...
12. To understand the physical meaning of the stiffness coefficient, ...
13. As a result of expressing the value of "k" we ...
14. From elementary school mathematics, we know that ...
15. The physical meaning of the stiffness coefficient is that it ...

The initial extension of the spring is A /. How to change
  potential spring energy if its elongation
  will be double?
  1) will increase by 2 times
  2) increase 4 times
3) decrease by 2 times
  4) decrease by 4 times
  Two bodies move in a mutually perpendicular transition.
straight lines, as shown in the figure. Module
  impulse of the first body p \\ =  8 kg-m / s, and the second body
p 2 =  6 kg-m / s. What is the module of body impulse,
  suspended as a result of their absolutely inelastic impact?
  Have
R \\
  1) 2 kg-m / s
  2) 48 kg-m / s
  3) 10 kg * m / s
  4) 14 kg-m / s
156

In the study of the dependence of the sliding friction force
A5
Fjp steel bar on the horizontal surface of the table
  by mass t  bar obtained graph presented on
  drawing According to the graph, in this study the coefficient
  friction friction is approximately equal
2) 0,02
3) 1,00
4) 0,20
  A car moving on a horizontal road
A6
  waving a turn along the arc of a circle. What is the minimum
  radius of this circle with the friction coefficient of the car
  mobile tires about road 0.4 and car speed
  10 m / s?
  1) 25 m
  2) 50 m
  3) 100 m
  4) 250 m
  For 2 straight linear motion body
A7
  passed 20 m, increasing its speed 3 times. Determine
  initial body speed.
  1) 5 m / s
  2) 10 m / s
  3) 15 m / s
  4) 30 m / s
157

The figure shows a graph of the process carried out over 1
  A8
  we pray perfect gas. Find the temperature ratio Zk
Tx
1) 6
4) 15
  The graph shows the dependence of pressure on concentration
  A9
  traction for two ideal gases at fixed
T
  temperatures. The ratio of the temperature p _J_ of these gases is
T2
1)
1
2)
2
3)
0,5
4)
7 2
  t-i -) -
4-4- .
-
  i i i
  c - -
  J -
  - - i. -
  H --- 1-
«
  I
  I
  I
  I
1
  I
  j __ 1__ 1 - 4 __ 1 __ I -
I G t 7\   R

  I I I I I
  -1-- g - + -I --- * -
  I I I I I I I
- J-
  І - - 4 - - i -
  I -
* . - 1 ------1------1--------
  "I ................
  t
  i
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P
158

A 10
  Crystal thing
using heat
  the heater was uniformly heated from
0
  before
  of the moment
t0.
  Then
  heater
  turned off.
  On
  the graph is represented depending
  temperature bridge T  substances
from time t.  Which plot with
corresponds to the process of heating a substance in a liquid state?
1) 5-6
2) 2-3
3) 3-4
4) 4-5
  Gas in a heat engine received an amount of heat 300 J
A p
  and accomplished work7 36 J. How has the internal energy changed
  gas?
  1) decreased by 264 j
  2) decreased by 336 J
  3) increased by 264 j
  4) increased by 336 J
A12
  The ideal gas was first heated at constant pressure.
then its pressure decreased at constant
  volume, then at constant temperature the volume of gas
decreased to the original value. Which gra
  fikov in coordinate axes p - V  matches this of
  gas state changes?
1)
3)
4) rl
but
v
v
  V
v
159

A13
  Two point electric charges act on each
friend with 9 micron forces. What will be the forces of interaction
between them if, without changing the distance between
  Dami, increase the modulus of each of them in 3 times?
  1) 1 μN
  2) 3 μN
  3) 27 μN
  4) 81 μN
  D 1 4
  A constant electric current flows through the conductor. Sign
  --- - The value of the charge passing through the conductor increases with
  over time according to the schedule presented on
drawing The current in the conductor is equal to
1) 1.5 A
  2) 4 A
  3) 6 A
  4) 24 A
  Using the fundamental law of electromagnetic
  induction (£
= -
) can be explained
  IVD
  d ^
  1) the interaction of two parallel wires, according to
  which is current
  2) the deviation of the magnetic needle located
  near a conductor with current parallel to it
  3) the occurrence of electric current in a closed
  coil when the current increases in another
  carcass next to her
  4) the occurrence of a force acting on a conductor with
  current in a magnetic field