Forces — practice question

Two forces of magnitudes $F_1$ and $F_2$ act on an object at right angles to one another. What is the magnitude of the resultant force?

• A$\sqrt{F_1^2 + F_2^2}$
• B$\sqrt{F_1} + \sqrt{F_2}$
• C$\sqrt{F_1^2} + \sqrt{F_2^2}$
• D$\sqrt{F_1 + F_2}$