Question

A force $(3i+4j)$ newton acts on a body and displaced it by $(3i+4j)$ metre. The work done by this force is:

• A. $10J$
  
• B. $5J$
  
• C. $25J$
  
• D. $12J$
  

Answer 1

The correct option is C $25J$

$Work=force\ast displacement=(3i+4j)(3i+4j)=3\ast 3i.i+4\ast 4j.j+4\ast 3i.j+4\ast 3i\ast j=9+16=25J$
as,$i.i=j.j=1;i.j=j.i=0$