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.
A
60 km hr\(^{-1}\)
B
8 km hr\(^{-1}\)
C
40 km hr\(^{-1}\)
D
56 km hr\(^{-1}\)
Verified Correct Answer: D.
Physical Principles & Numerical Solution
From momentum conservation
(800 x 80) + (1200 x 40)
= (800 + 1200) V
= 64000 + 48000 = 2000V
112000 = 2000V
V = \(\frac{112000}{2000}\)
= 56kmh\(^-1\)
The common velocity = 56kmhr\(^{-1}\)
Source: Myschool Past Questions Archive (Record #58901)