Mass of the dumbbell, m = 10 kg

Distance covered by the dumbbell, s = 80 cm = 0.8 m

Acceleration in the downward direction, a = 10 m/s^{2}

Initial velocity of the dumbbell, u = 0

Final velocity of the dumbbell (when it was about to hit the floor) = v

According to the third equation of motion:

v^{2}= u 2 + 2as

v^{2}= 0 + 2 (10) 0.8

v= 4 m/s

Hence, the momentum with which the dumbbell hits the floor is

= mv

= 10 × 4 kg m s^{-1}

= 40 kg m s^{-1}