Question

a group of students places a fan cart at one end of a track. when the fan is switched on, a constant force is exerted on the cart. the greater the fan’s speed, the stronger the force. the students can add or remove blocks to change the cart’s mass. their setup is modeled below. the students switch on the fan and release the cart. they measure the time it takes to reach the other end. the first time they try this, the cart moves very fast. which of the following changes would decrease the cart’s acceleration? choose 2 answers: a add more blocks to the cart b take some blocks off the cart c increase the fan’s speed d decrease the fan’s speed

Explanation:

To determine how to decrease the cart's acceleration, we use Newton's second law, \( F = ma \) (or \( a=\frac{F}{m} \)), where \( a \) is acceleration, \( F \) is force, and \( m \) is mass. Acceleration is directly proportional to force and inversely proportional to mass.

• Option A: Adding more blocks increases the cart’s mass (\( m \)). Since \( a=\frac{F}{m} \), increasing \( m \) (with \( F \) constant, assuming fan speed isn’t changed yet) decreases \( a \).
• Option B: Removing blocks decreases mass, which would increase acceleration (since \( a \) is inversely proportional to \( m \)), so this is incorrect.
• Option C: Increasing fan speed increases the force (\( F \)). Since \( a \) is directly proportional to \( F \), this would increase acceleration, so this is incorrect.
• Option D: Decreasing fan speed decreases the force (\( F \)). Since \( a \) is directly proportional to \( F \), decreasing \( F \) (with \( m \) constant) decreases \( a \).

Answer:

A. add more blocks to the cart
D. decrease the fan's speed