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Question
a basket of apples is pulled with a constant force. a friction force acts in a direction opposite to the motion. the basket starts at rest and increases its speed over time (accelerates). click on each action that will reduce the acceleration (rate at which the basket increases speed over time). options: a pull with less force, b pull with more force, c add an apple to the basket, d take an apple out of the basket, e smooth the surface of the table to decrease friction, f roughen the surface of the table to increase friction.
To solve this, we use Newton's second law \( F_{net} = ma \) (net force equals mass times acceleration) and analyze how each action affects net force or friction (which opposes motion, reducing net force):
Step 1: Recall Newton’s Second Law
Net force \( F_{net} = F_{pull} - F_{friction} \), and \( a = \frac{F_{net}}{m} \). To reduce acceleration, we need to reduce \( F_{net} \) (either by increasing friction, increasing mass, or decreasing the pulling force).
Analyze Each Option:
- Option A (pull with less force): Decreasing \( F_{pull} \) reduces \( F_{net} \) (since \( F_{net} = F_{pull} - F_{friction} \)). Lower \( F_{net} \) means lower acceleration (\( a = \frac{F_{net}}{m} \)). This reduces acceleration.
- Option B (pull with more force): Increases \( F_{pull} \), so \( F_{net} \) increases. Acceleration would increase, not decrease. Eliminate.
- Option C (add an apple to the basket): Increases mass (\( m \)). From \( a = \frac{F_{net}}{m} \), if \( F_{net} \) stays the same and \( m \) increases, \( a \) decreases. Wait, but let’s check other options. Wait, adding mass increases inertia, but does it affect net force? Wait, friction is \( F_{friction} = \mu N \), and \( N \) (normal force) equals weight (\( mg \)). So adding mass increases \( N \), which increases friction. Wait, no—wait, the basket is being pulled horizontally. Normal force \( N = mg \) (vertical). So adding mass increases \( m \), so \( N \) increases, so friction \( F_{friction} = \mu N \) increases. Also, mass \( m \) increases. Let’s re-express \( F_{net} = F_{pull} - \mu mg \), so \( a = \frac{F_{pull} - \mu mg}{m} = \frac{F_{pull}}{m} - \mu g \). If \( m \) increases, \( \frac{F_{pull}}{m} \) decreases, and \( \mu g \) is constant. So \( a \) decreases. But wait, the question is which action reduces acceleration. But let’s check Option E and F.
- Option D (take an apple out): Decreases mass (\( m \)). From \( a = \frac{F_{pull} - \mu mg}{m} = \frac{F_{pull}}{m} - \mu g \), decreasing \( m \) increases \( \frac{F_{pull}}{m} \), so \( a \) increases. Eliminate.
- Option E (smooth the table): Decreases friction (\( \mu \) decreases, since smoother surface has less friction). So \( F_{friction} = \mu mg \) decreases, so \( F_{net} = F_{pull} - F_{friction} \) increases. Acceleration increases. Eliminate.
- Option F (roughen the table): Increases friction (\( \mu \) increases). So \( F_{friction} \) increases, \( F_{net} \) decreases, so \( a \) decreases. Wait, but now we have two options (A, C, F?) Wait, no—let’s re-examine the problem statement: the basket is pulled with a constant force. Wait, the original scenario: “A basket of apples is pulled with a constant force. A friction force acts in a direction opposite to the motion. The basket starts at rest and increases its speed over time (accelerates).” We need to find which action reduces acceleration (i.e., makes it speed up more slowly, or even slow down, but since it’s accelerating initially, reducing acceleration means smaller positive acceleration).
Wait, let’s re-express \( a = \frac{F_{pull} - F_{friction}}{m} \).
- Option A (pull with less force): \( F_{pull} \) decreases → \( F_{net} \) decreases → \( a \) decreases.
- Option C (add an apple): \( m \) increases, and \( F_{friction} = \mu mg \) increases (since \( N = mg \) increases). So \( F_{net} = F_{pull} - \mu mg \). If \( m \) increases, both the numerator (\( F_{pull} - \mu mg \)) and denominator (\( m \)) change. Let’s take numbers: Suppose \( F_{pull} = 10 N \), \( \mu = 0.2 \),…
To reduce acceleration, we use \( F_{net} = ma \): acceleration is proportional to net force. Net force is \( F_{pull} - F_{friction} \).
- Option A: Pulling with less force decreases \( F_{pull} \), so \( F_{net} \) decreases → acceleration decreases.
- Option C: Adding an apple increases mass (\( m \)) and friction (\( F_{friction} = \mu mg \) increases), so \( F_{net} \) decreases → acceleration decreases.
- Option F: Roughening the table increases friction (\( \mu \) increases), so \( F_{friction} \) increases → \( F_{net} \) decreases → acceleration decreases.
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A. pull with less force, C. add an apple to the basket, F. roughen the surface of the table to increase friction
(If only one is required, the most direct is A. pull with less force.)