Question

Пуля летит горизонтально со скоростью u0=200 м/c, пробивает брусок, стоящий на горизонтальной поверхности льда , и продолжает движение в прежнем направлении со скоростью 1/4 u0. Масса бруска в 10 раз больше массы пули. Коэффициент трения скольжения между бруском и льдом мю=0,1. На какое расстояние S сместится брусок к моменту, когда его скорость уменьшиться на 20%?

Answer 1

 начальная скорость 15 а конечная 12

на листочках решения 

15*0.8=12 

Answer 2

Problem Analysis

We are given the following information: - A bullet is flying horizontally with an initial speed of u0 = 200 m/s. - The bullet penetrates a block of ice on a horizontal surface and continues moving in the same direction with a speed of 1/4 u0. - The mass of the block is 10 times greater than the mass of the bullet. - The coefficient of sliding friction between the block and the ice is μ = 0.1. - We need to find the distance S that the block will move by the time its speed decreases by 20%.

Solution

To solve this problem, we can use the principle of conservation of mechanical energy. The initial kinetic energy of the bullet is equal to the final kinetic energy of the bullet and the block combined.

Let's break down the solution into steps:

1. Calculate the initial kinetic energy of the bullet. 2. Calculate the final kinetic energy of the bullet and the block combined. 3. Equate the initial and final kinetic energies to find the velocity of the block. 4. Use the velocity of the block to calculate the distance it will move.

Step 1: Calculate the initial kinetic energy of the bullet

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

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

Given: - Mass of the bullet = m - Initial velocity of the bullet = u0

The initial kinetic energy of the bullet is:

Initial kinetic energy of the bullet = (1/2) * m * u0^2

Step 2: Calculate the final kinetic energy of the bullet and the block combined

The final kinetic energy of the bullet and the block combined can be calculated using the formula:

Kinetic energy = (1/2) * (mass of the bullet + mass of the block) * velocity^2

Given: - Mass of the bullet = m - Mass of the block = 10m - Final velocity of the bullet and the block combined = (1/4) * u0

The final kinetic energy of the bullet and the block combined is:

Final kinetic energy = (1/2) * (m + 10m) * ((1/4) * u0)^2

Step 3: Equate the initial and final kinetic energies to find the velocity of the block

Setting the initial and final kinetic energies equal to each other, we have:

(1/2) * m * u0^2 = (1/2) * (m + 10m) * ((1/4) * u0)^2

Simplifying the equation:

u0^2 = (1/4) * u0^2 * (11m)

Dividing both sides by u0^2:

1 = (1/4) * 11m

Simplifying further:

4 = 11m

Solving for m:

m = 4/11

Step 4: Use the velocity of the block to calculate the distance it will move

To calculate the distance the block will move, we need to find the time it takes for the block to decrease its speed by 20%. We can then use this time to calculate the distance using the formula:

Distance = velocity * time

Given: - Initial velocity of the block = (1/4)