Лабораторные работы / Решенная лабораторная по физике 03a

The laboratory work N^o 3,a.

Definition of the speed of a bullet with the help of a ballistic pendulum.

Had done by the student gr: 220473я F.N.S. Pavlov F.E.

Checked by ______________________ date ____________

Purpose: to define the speed of flight of a bullet using the laws of concervation of impulse and mechanical energy.

The order of performing a work:

1. To write meanings of masses bullet т₁ and pendulum т₂, length of thread l and it’s errors in to the table N^o1.

2. To insert a bullet into a stem of a spring pistol.

3. By pressing on the trigger to make a shot and to measure on the scale a angel of rejection of the pendulum from a vertical position(10 times).

4. To write meanings of the angel of rejection in to the table N^o2.

5. To define and write a average meaning the angel of rejection <>, the casual rejections _I, and average square rejection , where .

6. Under the formula to evaluate meaning of velocity of the bullet.

7. The attitude and absolute errors to evaluate by formulas: ; .

8. To wright the result in the form: m/s.

The bullet of weight m₁ driven in a horizontal direction with the velocity of V vector flys in the cylinder of a ballistic pendulum and jams in it. After the impact the cylinder of a pendulum of the weight m₂ together with the bullet, which has got stuck in it, gets some velocity U vector. On the basis of the law of conservation of the angular momentum, it is possible to write down:

And in a projection to an axis conterminous to a direction of a movement of the bullet and the pendulum with the bullet,

(1)

The system "pendulum-stucked bullet " has a kinetic energy (m + m) U/2, directly after the impact, which turns to potential energy (m + m)gh in process of a deviation of a pendulum from a vertical position. If we neglect the losses of energy during the friction, we receive

(2)

on the basis of the law of preservation of mechanical energy

Where h - the height of rise of the centre of weights of system "pendulum - bullet". From a figure follows, that

,

Where - is angle of a deviation of the pendulum from a vertical position; l - is length of the rope. From here follows :

Substituting h in the formula (2), we'll receive

(3)

Now substituting formula (3) in the formula (1), we'll get the velocity:

(4)

Table N^o1.

т1,kg	т1, kg	т2, kg	т2, kg	l, m	l, m
0.02	0.005	0.588	0.0005	0.96	0.005

Table N^o2.

	1	2	3	4	5	6	7	8	9	10	<i>
i	0.032	0.026	0.026	0.02	0.017	0.02	0.015	0.023	0.026	0.035	0.024
I	0.02

Table N^o3.

<V>, m/s	V, m/s	E, %
1.88	0.81	4.3

(1.880.81) m/s.

Conclusion: so we have studied to define the speed of flight of a bullet using the laws of concervation of impulse and mechanical energy.