Question

1. a 20,000 kg railroad car is coasting at 3 m/s when it collides and couples with a second, identical car at rest. what is the resulting speed of the combined cars? (a) 60,000 m/s (b) 0.00015 m/s (c) 0.9 m/s (d) 1.5 m/s (e) none of the above

Explanation:

Step1: Apply conservation of momentum

$m_1v_1=(m_1 + m_2)v_f$
Here, $m_1 = 20000$ kg, $v_1=3$ m/s, and $m_2 = 20000$ kg.

Step2: Substitute values

$(20000\times3)=(20000 + 20000)v_f$
$60000 = 40000v_f$

Step3: Solve for $v_f$

$v_f=\frac{60000}{40000}=1.5$ m/s

Answer:

D. 1.5 m/s