Question

Пуля массой 9 кг на скорости 900 м/с пробивает доску и вылетает из нее со скоростью 400 м/с. найти работу, совершенную над пулей силой сопротивления доски.

Answer 1

Работа равна смене кинетической енергии: A=Ek1-Ek2;
A=(m(U1)^2)/2 - (m(U2)^2)/2=(9*81*10^4)/2 - (16*10^4)/2 = 29,25*10^3=29,25кДж

Answer 2

Calculation of Work Done on the Bullet by the Resistance Force of the Board

To find the work done on the bullet by the resistance force of the board, we need to calculate the change in kinetic energy of the bullet as it passes through the board.

The initial kinetic energy of the bullet can be calculated using the formula:

Kinetic energy = (1/2) * mass * velocity^2

Given that the mass of the bullet is 9 kg and the initial velocity is 900 m/s, we can calculate the initial kinetic energy.

Initial kinetic energy = (1/2) * 9 kg * (900 m/s)^2

Next, we need to calculate the final kinetic energy of the bullet as it exits the board. The final velocity of the bullet is given as 400 m/s.

Final kinetic energy = (1/2) * 9 kg * (400 m/s)^2

The change in kinetic energy is the difference between the initial and final kinetic energies.

Change in kinetic energy = Final kinetic energy - Initial kinetic energy

Finally, the work done on the bullet by the resistance force of the board is equal to the change in kinetic energy.

Work done = Change in kinetic energy

Let's calculate the values:

Initial kinetic energy = (1/2) * 9 kg * (900 m/s)^2 = 3645000 J.

Final kinetic energy = (1/2) * 9 kg * (400 m/s)^2 = 720000 J.

Change in kinetic energy = Final kinetic energy - Initial kinetic energy = 720000 J - 3645000 J = -2925000 J.

Therefore, the work done on the bullet by the resistance force of the board is -2925000 J.

Please note that the negative sign indicates that the work done is against the motion of the bullet, which is consistent with the resistance force of the board.