A small block with mass 1 kg slides in a vertical circle of radius 0.5 m on the inside of a circular track. There is friction between the trac and the block. At the bottom of the block's path, the speed of the block is 5 m's and at the top of the block's path, the speed of the block 1 m's. In going from the bottom to the top of the track, how much work is done by the friction force on the block?

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### Understanding Work Done by Friction in a Circular Track

A small block with a mass of 1 kg slides in a vertical circle of radius 0.5 m on the inside of a circular track. There is friction between the track and the block. At the bottom of the block's path, the speed of the block is 5 m/s, and at the top of the block's path, the speed of the block is 1 m/s. The question is: "In going from the bottom to the top of the track, how much work is done by the friction force on the block?"

#### Answer Choices:
- O -11.3 J
- O 10.0 J
- O -9.90 J
- O Cannot be calculated from the given information
- O -2.20 J

#### Detailed Explanation:
To solve this problem, consider the following points:
- **Kinetic Energy at the Bottom:** \( KE_{bottom} = \frac{1}{2} m v^2 = \frac{1}{2} \times 1 \times 5^2 = 12.5 \, \text{J} \)
- **Kinetic Energy at the Top:** \( KE_{top} = \frac{1}{2} m v^2 = \frac{1}{2} \times 1 \times 1^2 = 0.5 \, \text{J} \)
- **Potential Energy at the Bottom:** It's zero since we are taking the bottom as the reference point \( PE_{bottom} = 0 \).
- **Potential Energy at the Top:** \( PE_{top} = mgh = 1 \times 9.8 \times 1 = 9.8 \, \text{J} \) (since the height difference \( h \) is 1 m, the diameter of the circle).

The work-energy principle states that:
\[ W_{\mathrm{friction}} = \Delta KE + \Delta PE \]

Substituting the values:
\[ W_{\mathrm{friction}} = (0.5 - 12.5) + (9.8 - 0) \]
\[ W_{\mathrm{friction}} = -12 + 9.8 \]
\[ W_{\mathrm{friction}} = -2.2 \, \text{J} \]

So, the correct answer is:
Transcribed Image Text:### Understanding Work Done by Friction in a Circular Track A small block with a mass of 1 kg slides in a vertical circle of radius 0.5 m on the inside of a circular track. There is friction between the track and the block. At the bottom of the block's path, the speed of the block is 5 m/s, and at the top of the block's path, the speed of the block is 1 m/s. The question is: "In going from the bottom to the top of the track, how much work is done by the friction force on the block?" #### Answer Choices: - O -11.3 J - O 10.0 J - O -9.90 J - O Cannot be calculated from the given information - O -2.20 J #### Detailed Explanation: To solve this problem, consider the following points: - **Kinetic Energy at the Bottom:** \( KE_{bottom} = \frac{1}{2} m v^2 = \frac{1}{2} \times 1 \times 5^2 = 12.5 \, \text{J} \) - **Kinetic Energy at the Top:** \( KE_{top} = \frac{1}{2} m v^2 = \frac{1}{2} \times 1 \times 1^2 = 0.5 \, \text{J} \) - **Potential Energy at the Bottom:** It's zero since we are taking the bottom as the reference point \( PE_{bottom} = 0 \). - **Potential Energy at the Top:** \( PE_{top} = mgh = 1 \times 9.8 \times 1 = 9.8 \, \text{J} \) (since the height difference \( h \) is 1 m, the diameter of the circle). The work-energy principle states that: \[ W_{\mathrm{friction}} = \Delta KE + \Delta PE \] Substituting the values: \[ W_{\mathrm{friction}} = (0.5 - 12.5) + (9.8 - 0) \] \[ W_{\mathrm{friction}} = -12 + 9.8 \] \[ W_{\mathrm{friction}} = -2.2 \, \text{J} \] So, the correct answer is:
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