Question

A body of mass 10 kg at rest is acted upon simultaneously by two forces 4N and 3N at right angles to each other. The kinetic energy of the body at the end of 10 sec is

• A. 100 J
• B. 300 J
• C. 50 J
• D. 125 J

Answer 1

Answer: (D)

125 J

Answer 2

As the forces are working at right angle to each other therefore net force on the body $F = \sqrt { 4 ^ { 2 } + 3 ^ { 2 } } = 5 N$

Kinetic energy of the body = work done = F × s

$= F \times \frac { 1 } { 2 } a t ^ { 2 } = F \times \frac { 1 } { 2 } \left( \frac { F } { m } \right) t ^ { 2 }$ $= 5 \times \frac { 1 } { 2 } \left( \frac { 5 } { 10 } \right) ( 10 ) ^ { 2 } = 125$J.