Question

Sketch a speed-time graph showing your trip from home to school.

A. Circle and label all the portion(s) of the graph where your car was an energy source during an interaction. Briefly explain how you reached that conclusion from the graph.

B. Circle and label all the portion(s) of the graph where your car was an energy receiver during an interaction. Briefly explain how you reached that conclusion from the graph.

C. Box and label all the portion(s) of the graph where unbalanced forces were acting on your car during an interaction. Briefly explain how you reach that conclusionfrom the graph.

D. Box and label all the portion(s) of the graph where balanced forces were acting on your car during an interaction. Briefly explain how you reached that conclusion from the graph.

Answer 1

Refer the figure above:

A. The car will be an energy source when car engine provides power and torque to counter the various opposing forces (drags) on the car. So, if the energy provided by car is just enough or greater than the energy taken up by drags, and in these cases speed will be constant (BC) or increasing (AB).

B. The car will be an energy receiver when without car power car gains speed. This can happen on a downhill, when gravitational potential energy (gradient is steep) would provide more energy to counter the various opposing forces (drags) on the car and the left over power will make the car gain speed. So, if the car is running downhill and the speed is increasing (AB when running downhill), then car is energy receiver.

C. If the the car has unbalanced forces i.e the total force on the car is non-zero, then car will be experience an acceleration or deceleration, and the speed will either increase (AB) or decrease (CD) respectively. This is because non-zero force means non-zero acceleration(positive or negative) and the speed will change.

D. If the the car has balanced forces i.e. the total force on the car is zero, then car will be moving with constant speed (BC) or is at rest (Point A and Point D). This is because no force means no acceleration and whatever the speed (zero or non-zero), it does not change.