WORK & energy

first of all we have to see that the dec in momentum is only due dec in velocity(mass is constant)
let mass be m nd original vel be v
v' be the changed velocity
mv=x
mv'=9x10
so vv'=910

% dec in KE=12mv² -12mv'²12mv² into 100

12 and m get cancelled
we are left with v²-v'²v² into 100
so the answer turns out be 10² -9²10² into 100
which is 19%

ans. D is correct..

(D)