An 800 kg car moving at 80 km hr\(^{-1}\) collides with a 1200 kg car moving at 40 km hr\(^{-1}\) in the same direction. If the cars stick together, calculate their common velocity.
60 km hr\(^{-1}\)
8 km hr\(^{-1}\)
40 km hr\(^{-1}\)
56 km hr\(^{-1}\)
Correct answer is B
From momentum conservation
(800 x 80) - (1200 x 40)
= (800 + 1200) V
= 64000 - 48000 = 2000V
16000 = 2000V
V = \(\frac{16000}{2000}\)
= 8kmh\(^-1\)
The common velocity = 8kmhr\(^{-1}\)