question_answer

A body moves a distance of 10 m along a straight line under a action of 5 N force. If work done is 25 J, then angle between the force and direction of motion of the body will be

A)  \[{{75}^{o}}\]                                   

B)  \[{{60}^{o}}\]                   

C)  \[{{45}^{o}}\]                   

D)         \[{{30}^{o}}\]

Correct Answer: B

Solution :

Key Idea: Component of force in the direction of displacement should be taken. Work is measured by the product of the applied force and the displacement of the body in the direction of the force Work = Force \[\times \]displacement                                 \[W=(Fcos\theta )\times \Delta s\] Given,   \[W=25\,J,F=5N,\Delta s=10\,m\] \[\cos \theta =\frac{W}{F.\Delta s}\] \[=\frac{25}{5\times 10}=\frac{1}{2}\]                 \[\Rightarrow \]               \[\theta ={{\cos }^{-1}}\left( \frac{1}{2} \right)={{60}^{o}}\] Hence, angle between force and direction of body is \[{{60}^{o}}.\]