Skip to content
Exercise 10.2 · Q2

Q.Write two different vectors having same magnitude.

Uttarakhand UbseTextbookSubjective· 2mImportance★★★★★
5% · 7/153 Questions
✓ Free question

The key idea is that magnitude depends only on the squares of the components, not on their signs or order. So two vectors like a⃗=(1,2,3)\vec{a} = (1, 2, 3) and b⃗=(−1,2,3)\vec{b} = (-1, 2, 3) both have magnitude 14\sqrt{14}.

The magnitude (or length) of a vector v⃗=(x,y,z)\vec{v} = (x, y, z) is given by ∣v⃗∣=x2+y2+z2|\vec{v}| = \sqrt{x^2 + y^2 + z^2}. This formula depends only on the squares of the components. That means if you change the sign of any component, or rearrange the components, the sum of squares stays the same — as long as the set of absolute values is unchanged.

So to get two different vectors with the same magnitude, you can:

  1. Flip signs: Take a⃗=(1,2,3)\vec{a} = (1, 2, 3). Its magnitude is 12+22+32=14\sqrt{1^2 + 2^2 + 3^2} = \sqrt{14}. Now take b⃗=(−1,2,3)\vec{b} = (-1, 2, 3). Its magnitude is (−1)2+22+32=1+4+9=14\sqrt{(-1)^2 + 2^2 + 3^2} = \sqrt{1 + 4 + 9} = \sqrt{14}. They are different vectors (point in opposite directions along the x-axis) but have the same length.

  2. Permute components: Another pair: c⃗=(1,2,3)\vec{c} = (1, 2, 3) and d⃗=(3,1,2)\vec{d} = (3, 1, 2). Both have magnitude 14\sqrt{14} because the sum of squares is 1+4+91+4+9 in both cases.

Tip

In 2D, a classic example is p⃗=(3,4)\vec{p} = (3, 4) and q⃗=(−3,−4)\vec{q} = (-3, -4) — both have magnitude 55. Or even r⃗=(5,0)\vec{r} = (5, 0) and s⃗=(0,5)\vec{s} = (0, 5) — both have magnitude 55, but are perpendicular.

Watch out

A common mistake is to think that if two vectors have the same magnitude, they must be equal or opposites. Not true — as the permutation example shows, they can be completely unrelated in direction.

✓Final answer

Two such vectors are a⃗=(1,2,3)\vec{a} = (1, 2, 3) and b⃗=(−1,2,3)\vec{b} = (-1, 2, 3), both with magnitude 14\sqrt{14}.

Unlock everything free for 14 days

  • Full step-by-step solutions
  • Concept-first explanations
  • Methods, shortcuts & mistakes
  • PYQ mapping + timed mock tests

Full access for 14 days. No credit card required.