Question

If force $\vec{ F }= 5 \hat{ i }+3 \hat{ j }+4 \hat{ k }$ makes a displacement of $\vec{ s }=6 \hat{ i }-5 \hat{ k }$, work done by the force is :

• A. 10 unit
• B. $122\sqrt{5}$ unit
• C. $5\sqrt{122}$ unit
• D. 20 unit

Answer 1

Answer: (A)

10 unit

Answer 2

Work done $=\vec{ F } \cdot \vec{ s }$ $=(5 \hat{ i }+3 \hat{ j }+4 \hat{ k }) \cdot(6 \hat{ i }-5 \hat{ k })$ $=(5 \hat{ i }+3 \hat{ j }+4 \hat{ k }) \cdot(6 \hat{ i }+0 \hat{ j }-5 \hat{ k })$ $=(30+0-20)=10$ unit