Mass of the air-track glider, ma=0.2 kg
Spead of the air-track glider, v1=1.20 m/s
Mass of bumps = 0.60 kg
Spead of the bumps, v1= 0
An elastic collision conserves mechanical energy
KE= 1/2 ma*v1^2
Substitute 1.20 for v1 and 0.20 for ma
1/2 0.20 (1.20)^2
=0.144 J
Totally inellastic collision coservation of momentum
M1V1 +M2V2= (M1M2)V3
0.20(1.20)+0.600= 0.800(V3)
V3= 0.300
So
KE= 1/2 mv^2
1/2 (0.800)(0.300)^2= 0.036 J
Notice that 3/4 of the original KE is lost in this collision.