Question

Поезд массой 1200 т тормозит. Начальная скорость при торможении 72 км в час, тормозной путь 3 км. Найти работу силы трения. С решением и пояснением.

Answer 1

Дано m=1200 000 кг   V=72 км/ч=20 м/с    s=3000 м   Атр- ?

по теореме об изменении кинетической энергии Атр=E-Eo=-m*V^2/2=-1200000*400/2=-240000000Дж

Answer 2

Calculation of Frictional Force

To find the frictional force acting on the train, we can use the equation:

Frictional Force = Mass * Acceleration

Given: - Mass of the train = 1200 t (tonnes) - Initial velocity = 72 km/h - Deceleration (negative acceleration) = -Acceleration - Deceleration = Change in velocity / Time taken - Time taken = Distance / Velocity

We are given the deceleration and the initial velocity, so we can calculate the time taken to come to rest using the formula:

Time taken = Change in velocity / Deceleration

The change in velocity is the difference between the initial velocity and the final velocity, which is 0 in this case since the train comes to rest.

Let's calculate the time taken:

Change in velocity = 0 - 72 = -72 km/h

Now, we need to convert the velocity from km/h to m/s:

Change in velocity = -72 km/h * (1000 m/3600 s) = -20 m/s

Now, we can calculate the time taken:

Time taken = -20 m/s / Deceleration

The deceleration is given by:

Deceleration = -Change in velocity / Time taken

Given that the deceleration is constant, we can use the average velocity during deceleration to calculate the time taken. The average velocity is the average of the initial and final velocities, which is half of the initial velocity in this case.

Average velocity = 72 km/h / 2 = 36 km/h

Converting the average velocity to m/s:

Average velocity = 36 km/h * (1000 m/3600 s) = 10 m/s

Now, we can calculate the time taken:

Time taken = -20 m/s / (-10 m/s) = 2 seconds

The distance traveled during deceleration is given by:

Distance = Initial velocity * Time taken + (1/2) * Deceleration * (Time taken)^2

Substituting the given values:

Distance = 72 km/h * (1000 m/3600 s) * 2 s + (1/2) * Deceleration * (2 s)^2

Simplifying:

Distance = 40 m + Deceleration * 4 m

Given that the distance is 3 km, we can convert it to meters:

Distance = 3 km * (1000 m/1 km) = 3000 m

Equating the two distances:

3000 m = 40 m + Deceleration * 4 m

Simplifying:

Deceleration = (3000 m - 40 m) / 4 m

Deceleration = 740 m/s^2

Now, we can calculate the frictional force:

Frictional Force = Mass * Deceleration

Substituting the given values:

Frictional Force = 1200 t * 740 m/s^2

Converting the mass from tonnes to kilograms:

Frictional Force = 1200 t * (1000 kg/1 t) * 740 m/s^2

Simplifying:

Frictional Force = 888000000 N

Therefore, the frictional force acting on the train is 888,000,000 N.

Answer:

The frictional force acting on the train is 888,000,000 N.