jmc

We need to find square factors of 2940. Beginning the search, we can first see it is divisible by 10. So, $2940=2\cdot 5\cdot 294$. Looking at 294, we can see it is divisible by 2 and 3. Taking out these factors, find that $294=2\cdot 3\cdot 49$. Since $49=7^2$, there is a square factor of 2 and a square factor of 7. The complete factorization is $2940=2^2\cdot 3\cdot 5\cdot 7^2$. Therefore, $$\sqrt{2940}=\sqrt{2^2\cdot 3\cdot 5\cdot 7^2}=2\sqrt{3\cdot 5\cdot 7^2}=2\cdot 7\sqrt{3\cdot 5}=\boxed{14\sqrt{15}}$$