Question

students are using the experimental setup shown in the image in which the two ends of a string are attached to a car and to a hanger. the students conduct three trials in which they place metal discs on the hanger to manipulate the force applied to the car. as a result, the car accelerates along the table while two probes collect motion data.

on the fourth trial of this experiment, a student places some discs on the car by mistake. how would this change the acceleration or velocity?

(2 points)

in comparison to the third trial, when the student adds discs to the car instead of the hanger, the mass of the car is decreased, which will decrease the acceleration of the car across the table.

in comparison to the third trial, when the student adds discs to the car instead of the hanger, the mass of the car is increased, which will decrease the acceleration of the car across the table.

in comparison to the third trial, when the student adds discs to the car instead of the hanger, the mass of the car is decreased, which will increase the acceleration of the car across the table.

in comparison to the third trial, when the student adds discs to the car instead of the hanger, the mass of the car is increased, which will increase the acceleration of the car across the table.

Explanation:

To solve this, we use Newton's second law \( F = ma \) (where \( F \) is force, \( m \) is mass, \( a \) is acceleration). The force here is mainly from the hanger's weight. When discs are added to the car, the car's mass (\( m \)) increases. Since force (\( F \)) from the hanger (assuming hanger's mass change is negligible or not considered here) is approximately constant, from \( a=\frac{F}{m} \), if \( m \) increases, \( a \) decreases. Let's analyze each option:

• First option: Says mass of car is decreased (wrong, adding discs increases mass) and acceleration decreases (but mass change is wrong). Eliminate.
• Second option: Mass of car is increased (correct, adding discs) and acceleration decreases (since \( a=\frac{F}{m} \), larger \( m \) with same \( F \) gives smaller \( a \)). This matches.
• Third option: Mass decreased (wrong) and acceleration increased (wrong). Eliminate.
• Fourth option: Mass increased (correct) but acceleration increased (wrong, as \( a \) should decrease with larger \( m \) for same \( F \)). Eliminate.

Answer:

B. In Comparison to the third trial, when the student adds discs to the car instead of the hanger, the mass of the car is increased, which will decrease the acceleration of the car across the table.