Prime factorising 10976, we get,
10976=2×2×2×2×2×7×7×7
=25×73.
We know, a perfect cube has multiples of 3 as powers of prime factors.
Here, number of 2's is 5 and number of 7's is 3.
So we need to multiply another 2 to the factorization to make 10976 a perfect cube.
Hence, the smallest number by which 10976 must be multiplied to obtain a perfect cube is 2.