A225 kg red bumper car is moving at 3.0 m/s. it hits a stationary 180 kg blue bumper car. the red and blue bumper cars combine and hit a stationary green bumper car of mass 150 kg. the red, blue, and green bumper cars all combine.
a. 0.93 m/s
b 1.2 m/s
c 1.7 m/s
d 2.7 m/s

B. 1.2m/s

Explanation:

as per the law of conservation of momentum,

initial momentum= final momentum

considering collision 1 : Mr * Vr + ( Mb * Vb) = ( Mr + Mb ) Vrb

where Vrb is the final velocity after 1st collision with which red and blue car moves.

therefore,  225* 3 + 0 = ( 225 + 180 ) Vrb

Vrb = 675/405

       = 1.67m/s

now collision 2 : ( Mr+ Mb) Vrb + MgVg= ( Mr+ Mg+ Mb ) V'

where V' is the total speed

675 + 0 = 555V'

V' = 675/555

   = 1.2 m/s

explanation:

v=uf/(u-f)

= 5.-10/(5+10) convex lens has negative focal length

d.7.5cm is your answer