Moderate -0.3 This is a straightforward application of the power-force-velocity relationship (P = Fv) combined with Newton's second law (F = ma). Students must recognize that driving force minus resistance equals net force, then solve algebraically. It requires connecting two standard formulas but involves no complex problem-solving or novel insight—slightly easier than average due to its direct, single-concept nature.
1 A car of mass 800 kg is moving on a straight horizontal road with its engine working at a rate of 22.5 kW . Find the resistance to the car's motion at an instant when the car's speed is \(18 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) and its acceleration is \(1.2 \mathrm {~m} \mathrm {~s} ^ { - 2 }\).
1 A car of mass 800 kg is moving on a straight horizontal road with its engine working at a rate of 22.5 kW . Find the resistance to the car's motion at an instant when the car's speed is $18 \mathrm {~m} \mathrm {~s} ^ { - 1 }$ and its acceleration is $1.2 \mathrm {~m} \mathrm {~s} ^ { - 2 }$.
\hfill \mbox{\textit{CAIE M1 2014 Q1 [4]}}