A 8000 kg engine pulls a train of 5 wagons, each of 2000 kg, along a horizontal track. If the engine exerts a force of 40000 N and the track offers a friction force of 5000 N, then calculate: (a) the net accelerating force and (b) the acceleration of the train.
Solution and Explanation
(a) Net accelerating force = Force exerted by engine–Friction force (Here frictional force is subtracted because it opposes the motion) = 40000 –5000 = 35000 N = 3.5 × 104N
(b) From Newton's second law of motion, Accelerating force = Mass of the train × Acceleration of train a = F ---- m Mass of train = Mass of engine + Mass of all wagons = 8000 + 5 × 2000 = 8000 + 10000 = 18000 kg Acceleration = 35000 = 35 = 1.95ms-2
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Concepts Used:
Laws of Motion
The laws of motion, which are the keystone of classical mechanics, are three statements that defined the relationships between the forces acting on a body and its motion. They were first disclosed by English physicist and mathematician Isaac Newton.
Newton’s First Law of Motion
Newton’s 1st law states that a body at rest or uniform motion will continue to be at rest or uniform motion until and unless a net external force acts on it.
Newton’s Second Law of Motion
Newton's 2nd law of motion deals with the relation between force and acceleration. According to the second law of motion, the acceleration of an object as built by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.
Newton’s Third Law of Motion
Newton's 3rd law of motion states when a body applies a force on another body that there is an equal and opposite reaction for every action.