Answer:
firstly,
ke=1÷2mv^2
on putting same ke by increasing mass by 16 times new velocity becomes v'
then
ke=1÷2×16m×v'^2
from above we can write
1÷2mv^2=1÷2×16m×v'^2
v^2=16v'^2
1÷4v=v'
hence original velocity should be decreased by 4 times to keep same ke