A \(25 N\) force pulls a \(2.0 kg\) body up a \(30^{\circ}\) inclined plane. If the force is parallel to the plane and the body moves up the plane at constant velocity, calculate the magnitude of the frictional force between the body and the plane. \([g=\) \(10 m / s ^{2}\) ]
A. \(35 N\) B. \(25 N\) C. \(20 N\) D. \(15 N\)
Correct Answer: D
Explanation
It is said in the question that the body moves up the plane at constant velocity. How possible? This is only possible when the resulting force on the body is zero. \({\left[\left(\begin{array}{c}\text { Frictio- } \\ \text { nal force }\end{array}\right)+\left(\begin{array}{c}\text { compon- } \\ \text { ent of mg } \\ \text { down the } \\ \text { plane }\end{array}\right)\right]-25=0 }\) \(F r+m g \sin 30^{\circ}-25=0\) \(F r+20 \sin 30^{\circ}-25=0\) \(F r=0+25-20 \sin 30^{\circ}=15 N\)
