College Physics
11th Edition
ISBN: 9781305952300
Author: Raymond A. Serway, Chris Vuille
Publisher: Cengage Learning
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Transcribed Image Text:### Physics Problem Set: Forces on an Immovable Object
---
**Scenario:**
Lili pushes an 80-kg fridge on a horizontal surface with a pushing force of 200 N to the right, as shown in the diagram. The fridge does not move. The coefficients of friction between the floor and the fridge are μs (static friction coefficient) = 0.75 and μk (kinetic friction coefficient) = 0.40. Use \( g = 10 \, m/s^2 \). Match the answers with the questions.
**Diagram:**
- The diagram shows a figure pushing a fridge to the right on a tiled floor.
**Questions:**
1. **What is the magnitude and direction of the weight force on the fridge from the earth?**
2. **What is the magnitude and direction of the pushing force on the fridge from the hand?**
3. **What is the magnitude and direction of the normal force on the fridge from the floor?**
4. **What is the magnitude and direction of the friction force on the fridge from the floor?**
5. **What is the net force on the box?**
**Potential Answers:**
- A. 800 N, to the left
- B. 600 N, to the left
- C. None of the given
- D. 800 N, to the right
- E. 200 N, upward
- F. 800 N, upward
- G. 200 N, to the right
- H. 200 N, to the left
- I. 600 N, to the right
- J. 200 N, downward
- K. 800 N, downward
- L. Zero, therefore no direction
**Explanation of the Diagram:**
- The diagram depicts a person pushing a fridge to the right, illustrating the forces acting on the fridge. The fridge remains stationary because the pushing force is balanced by the friction force.
**Solution Method:**
1. **Weight Force (gravity):**
- \( \text{Weight} = \text{mass} \times \text{gravitational acceleration} \)
- \( \text{Weight} = 80 \, \text{kg} \times 10 \, \text{m/s}^2 \)
- Weight = 800 N, directed downward.
- Answer: K. 800 N, downward.
2
![### Understanding Friction Forces
#### Problem Statement:
A robot pushes a 20-kg box on the horizontal surface as part of the moving job. The force applied is 35 N to the left. The box does not move. The coefficients of friction between the floor and box are:
- Static friction coefficient (μₛ) = 0.75
- Kinetic friction coefficient (μₖ) = 0.40
**Question:** What is the direction of the friction force on the box?
#### Multiple-Choice Options:
- up
- none of the given
- down
- to the left
- to the right
#### Explanation:
In the image, we can see a robot pushing a box to the left. Despite the applied force, the box remains stationary, indicating that static friction is at play. Let's determine the frictional force.
**Step-by-Step Solution:**
1. **Calculate the maximum static friction:**
\[ F_{max\_static} = \mu_s \times N \]
Where:
- \( \mu_s = 0.75 \)
- \( N \) is the normal force, which equals the weight of the box since the surface is horizontal.
- Weight \( (W) = mg = 20 \, \text{kg} \times 9.8 \, \text{m/s}^2 = 196 \, \text{N} \)
Thus,
\[ F_{max\_static} = 0.75 \times 196 \, \text{N} = 147 \, \text{N} \]
2. **Compare the applied force with the maximum static friction force:**
- The applied force is 35 N, which is less than the maximum static friction force (147 N).
Because the force of friction is sufficient to counteract the applied force and the box does not move, the static friction force must be acting in the direction opposite to the force applied by the robot.
**Conclusion:**
- The frictional force on the box is 35 N to the right.
**Correct Answer:** to the right
### Visual Interpretation:
The diagram shows a robot on the right side of a box, attempting to push it to the left across a horizontal surface. The box does not move, which implies that the frictional force counteracts the applied force, and thus, the direction of the frictional force is to the right](https://content.bartleby.com/qna-images/question/22e3fc62-a2ed-46b5-9f14-7888cf9520df/8697400e-c941-435f-a9d9-8d6571eedd17/mldyx3sj_processed.png)
Transcribed Image Text:### Understanding Friction Forces
#### Problem Statement:
A robot pushes a 20-kg box on the horizontal surface as part of the moving job. The force applied is 35 N to the left. The box does not move. The coefficients of friction between the floor and box are:
- Static friction coefficient (μₛ) = 0.75
- Kinetic friction coefficient (μₖ) = 0.40
**Question:** What is the direction of the friction force on the box?
#### Multiple-Choice Options:
- up
- none of the given
- down
- to the left
- to the right
#### Explanation:
In the image, we can see a robot pushing a box to the left. Despite the applied force, the box remains stationary, indicating that static friction is at play. Let's determine the frictional force.
**Step-by-Step Solution:**
1. **Calculate the maximum static friction:**
\[ F_{max\_static} = \mu_s \times N \]
Where:
- \( \mu_s = 0.75 \)
- \( N \) is the normal force, which equals the weight of the box since the surface is horizontal.
- Weight \( (W) = mg = 20 \, \text{kg} \times 9.8 \, \text{m/s}^2 = 196 \, \text{N} \)
Thus,
\[ F_{max\_static} = 0.75 \times 196 \, \text{N} = 147 \, \text{N} \]
2. **Compare the applied force with the maximum static friction force:**
- The applied force is 35 N, which is less than the maximum static friction force (147 N).
Because the force of friction is sufficient to counteract the applied force and the box does not move, the static friction force must be acting in the direction opposite to the force applied by the robot.
**Conclusion:**
- The frictional force on the box is 35 N to the right.
**Correct Answer:** to the right
### Visual Interpretation:
The diagram shows a robot on the right side of a box, attempting to push it to the left across a horizontal surface. The box does not move, which implies that the frictional force counteracts the applied force, and thus, the direction of the frictional force is to the right
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