An eighth-grade class is studying the motion of objects. They have learned the following concepts about motion. Motion occurs when there is a change in the position of an object with respect to a reference point.

While the speed of the object may change at various times during a trip the average speed for the trip is found by dividing the total distance by the total time.

The motion of the object can be changed by varying the amount of net force acting on the object or by varying the mass of the object.

The teacher asked students to design investigations to determine how changing the forces acting on an object or the mass of the object would change its motion.

The materials for the investigation included:

1 - toy cart

3 - 10N weights

1 - pulley

2 - meters of string

One group of students decided to design an investigation to determine how different amounts of mass on the toy cart would affect the speed of the toy cart. They set up their investigation as shown below:

The students performed several trials using different masses in the toy cart (M1). They hung a mass shown as (M2) to pull the toy cart as it dropped.

Below is a table they made to record their results.

What other step do they need to add to their experimental design in order to determine the effect of mass on the speed of the toy cart?

A) Investigate the time it takes a different toy cart to travel for each trial.

B) Determine the total distance the toy cart traveled for each trial.

C) Determine the effect of increasing the force pulling the toy cart.

D) Investigate how much force was used on the toy cart for each trial.