Question

A 40,000 kg railroad car initially traveling at 10 m/s collides inelastically with a 20,000 kg railroad car initially at rest. The cars stick together. What is their final speed?

Answer 1

Answer on Question #41965 - Physics - Mechanics | Kinematics | Dynamics

A 40,000 kg railroad car initially traveling at 10 m/s collides inelastically with a 20,000 kg railroad car initially at rest. The cars stick together. What is their final speed?

Solution:

Given:

\begin{array}{l} = 40000 \text{ kg}, \\ \quad_{2} = 20000 \text{ kg}, \\ v_{i} = 10 \text{ m/s}, \\ v_{2i} = 0, \\ v_{f} = ? \end{array}

The equation that denotes the conservation of momentum is:

v_{i} + \quad_{2} v_{2i} = (m + \quad_{2}) v_{f}

where, $m_1 =$ mass of object or body 1

$m_2 =$ mass of object or body 2

$v_{i} =$ initial velocity of object or body 1

$v_{2i} =$ initial velocity of object or body 2

$v_{f} =$ final velocity of both the objects

The final velocity is given by

v_{f} = \frac{v_{i} + \quad_{2} v_{2i}}{2} $$v_{f} = \frac{40000 \cdot 10}{40000 + 20000} = \frac{20}{3} = 6.67 \text{ m/s}$$

Answer. $v_{f} = 6.67 \text{ m/s}$

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