The 15Mg booster A is coasting at 15 ms on the horizontal tr

The 15-Mg booster A is coasting at 1.5 m/s on the horizontal track when it encounters a 12-Mg tank car B coasting at 0.75 m/s toward it as shown. If the cars sheet and couple together, determine: the speed of both cars just after the coupling. The average force between them is the coupling takes place in 0.8 sec

Solution

a) from conservation of linear momentum,
   15 x 1.5 - 12 x 0.75 = (15+12) x v
=> v = 0.5 m/s

b) Average force is same on both bodies.
   Average force = ( change of momentum ) / 0.8 sec
   = 15 x 1000 kg x ( 1.5 - 0.5 ) / 0.8 = 18750 N