A toy has a battery-powered fan attached to it such that the fan creates a constant force that is exerted on the car so that it is propelled in the opposite direction in which the fan blows air. The car has carriage that allows a student to attach object of different masses,  as shown above. The fan has only one speed setting. All frictional forces are considered to be negligible. Which of the following procedures could be used to determine how the mass of the fan-car-object system affects the acceleration of the system?

a. Measure the mass of the system using a balance, activate the fan, measure the distance traveled by the system at a known time by using a stopwatch, and repeat the experiment for several trials with different added to the carriage.

b. Measure the mass of system using a balance, activate the fan, use a meterstick and stopwatch to measure the initial and final speeds of the system, and repeat the experiment for several trials with different objects added to the carriage.

c. Measure the mass of the system using a balance, connect a spring scale to the back of the car, measure the amount of force required to hold the system at rest, and repeat the experiment for several trial with different objects added to the carriage.

d. Measure the mass of system using a balance, activate the fan, use stopwatch to record the time it takes for the system to travel before the battery of the fan no longer works, and repeat the experiment for the trials with different objects added to the carriage.

Masses