Problem 14 A 15 kg box is initially sliding across a frictionless floor with a constant speed of 2.5 m/s. Then, the box encounters a rough surface and travels for 12 meters before coming to a stop. What is the coefficient of kinetic friction between the box and rough surface?

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### Problem 14

A 15 kg box is initially sliding across a frictionless floor with a constant speed of 2.5 m/s. Then, the box encounters a rough surface and travels for 12 meters before coming to a stop. What is the coefficient of kinetic friction between the box and rough surface?

### Solution Explanation

1. **Given**:
   - Mass of the box, \( m = 15 \, \text{kg} \)
   - Initial velocity, \( v_i = 2.5 \, \text{m/s} \)
   - Final velocity, \( v_f = 0 \, \text{m/s} \) (the box stops)
   - Distance traveled on rough surface, \( d = 12 \, \text{m} \)

2. **Looking for**: 
   - The coefficient of kinetic friction, \( \mu_k \)

3. **Using the equation of motion**:
   \[
   v_f^2 = v_i^2 + 2a d
   \]
   Rearrange to find acceleration \( a \):
   \[
   0 = (2.5)^2 + 2a \cdot 12
   \]

4. **Solve for acceleration** \( a \):
   \[
   -6.25 = 24a
   \]
   \[
   a = -\frac{6.25}{24}
   \]

5. **Using frictional force equation**:
   - The frictional force \( F_f = \mu_k \cdot N \) where \( N = m \cdot g \) (normal force)
   - Since \( F_f = m \cdot a \), substitute:
   \[
   \mu_k \cdot (15 \cdot 9.8) = 15 \cdot a
   \]
   Solve for \( \mu_k \):
   \[
   \mu_k = -\frac{a}{9.8}
   \]

By solving these equations, the coefficient of kinetic friction \( \mu_k \) can be determined.
Transcribed Image Text:### Problem 14 A 15 kg box is initially sliding across a frictionless floor with a constant speed of 2.5 m/s. Then, the box encounters a rough surface and travels for 12 meters before coming to a stop. What is the coefficient of kinetic friction between the box and rough surface? ### Solution Explanation 1. **Given**: - Mass of the box, \( m = 15 \, \text{kg} \) - Initial velocity, \( v_i = 2.5 \, \text{m/s} \) - Final velocity, \( v_f = 0 \, \text{m/s} \) (the box stops) - Distance traveled on rough surface, \( d = 12 \, \text{m} \) 2. **Looking for**: - The coefficient of kinetic friction, \( \mu_k \) 3. **Using the equation of motion**: \[ v_f^2 = v_i^2 + 2a d \] Rearrange to find acceleration \( a \): \[ 0 = (2.5)^2 + 2a \cdot 12 \] 4. **Solve for acceleration** \( a \): \[ -6.25 = 24a \] \[ a = -\frac{6.25}{24} \] 5. **Using frictional force equation**: - The frictional force \( F_f = \mu_k \cdot N \) where \( N = m \cdot g \) (normal force) - Since \( F_f = m \cdot a \), substitute: \[ \mu_k \cdot (15 \cdot 9.8) = 15 \cdot a \] Solve for \( \mu_k \): \[ \mu_k = -\frac{a}{9.8} \] By solving these equations, the coefficient of kinetic friction \( \mu_k \) can be determined.
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