27. Two trains, 1 and 2 , have an equal mass of \( m=5,000 \mathrm{~kg} \) each. Train 1 is traveling with a speed \( n=15 \mathrm{~m} / \mathrm{s} \) before striking train 2 , which was at rest. If the two trains lock together as the result of the collision. What is their common speed immediately after collision?

\( \begin{array}{l}\text { Ejemplo } 2 \\ \text { Encontremos la velocidad de una bala de } 0.02 \mathrm{~kg} \text { que adquiere una } \\ \text { energía cinética de } 400 \mathrm{~J} \text {. } \\ \text { Datos: } \\ m=0.02 \mathrm{~kg} \\ E_{h}=400 \mathrm{~J}=\frac{1}{2} m v^{2} \\ v=x\end{array} \quad \frac{2 E_{k}}{\mathrm{~m}}=v^{2} \quad \begin{array}{l}\text { Despejamos la velocidad dejándola } \\ \text { uno de los lados de la ecuación. }\end{array} \)

A 10 kg crate is placed on a rough horizontal surface \( \mu_{\mathrm{k}}=0.4 \) and connected with 12 kg hanging mass via a string that passes over a massless and frictionless pully as shown in the figure beside. Thé mass ( kg ) that must be added to the crate so that the crate moves with constant velocity is:

A lamp hangs vertically from a cord in a descending elevator that accelerates at \( 2.4 \mathrm{~m} / \mathrm{s}^{2} \). If the tension in the cord is 89 N . The mass of the lamp in \( (\mathrm{kg}) \) is:

Аанное уравнение: \[ \vec{a}=\sum_{k=1}^{n} \overrightarrow{F_{k}}+\vec{\Phi}_{e}+\vec{\Phi}_{C} \] называется: Выберите один ответ: Уравнением относительного двикения точки. Основным законом динамики относительного движения точки. Основным законом динамики линейного движения тела. Кориолисовой силой инерции.

A \( 20-\mathrm{m} \) long steel wire (cross-section \( 1 \mathrm{~cm}^{2} \), Young's modulus \( 2 \times 10^{11} \mathrm{~N} / \mathrm{m}^{2} \) ), is subjecte to a load of \( 25,000 \mathrm{~N} \). How much will the wire stretch under the load? \( \begin{array}{lllll}\text { A) } 0.25 & \text { B) } 2.5 \mathrm{~cm} & \text { C) } 12.5 \mathrm{~cm} & \text { D) } 25 \mathrm{~cm} & \text { E) } 1.25\end{array} \)