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

Correct Answer:

Option B – 8 km hr‾¹

Explanation

From momentum conservation

(800 x 80) – (1200 x 40)

= (800 + 1200) V

= 64000 – 48000 = 2000V

16000 = 2000V

V = 16000/2000

= 8kmh‾¹

The common velocity = 8kmhr‾¹