A particle moves 3m along the straight line x-y+8=0 with constant speed under the influence of a constant force F→=ai^−3j^N. Then the value of ‘a’ is

x−y+8=0⇒y=x+8. So the angle between the straight line and positive x-axis is 45o. ∴ Displacement d→=3cos45oi^+3sin45oj^m⇒d→=32i^+j^mSince the speed remains constant, change in kinetic energy is zero, hence work done by the force is zero. ∴ F→.d→=0⇒ai^−3j→.32i^+j^=0⇒a−3=0⇒a=3