# Suppose Justin, with a mass of 55 kg, is going down an 8.0-m-high water slide. He starts at rest,...

## Question:

Suppose Justin, with a mass of 55 kg, is going down an 8.0-m-high water slide. He starts at rest, and his speed at the bottom is 12 m/s. How much thermal energy is created by friction during his descent?

## Conservation Law of Energy:

Imagine a perfectly isolated system that contains a collective amount of energy (E). As per the conservation law of energy, this energy will be unchanged or remain constant. Although, the forms of this energy can be changed.

## Answer and Explanation:

**Given data:**

- Mass of Justin, {eq}m = 55 \ kg {/eq}

- Vertical height of the water slide, {eq}h = 8.0 \ m {/eq}

- Initial speed, {eq}u = 0 {/eq}

- Final speed, {eq}v = 12 \ m/s {/eq}

Let the magnitude of the thermal energy released in the process be ** Q**.

From the conservation law of energy,

{eq}U_{i} + K_{i} = U_{f} + K_{f} + Q\\ mgh + \frac{1}{2}mu^{2} = mgh' + \frac{1}{2}mv^{2} + Q\\ 55 \times 9.80 \times 8.0 + \frac{1}{2} \times 55 \times (0)^{2} = 55 \times 9.80 \times 0 + \frac{1}{2} \times 55 \times (12)^{2} + Q\\ \Rightarrow \ Q = 352 \ \rm J.\\ {/eq}

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from ICSE Environmental Science: Study Guide & Syllabus

Chapter 1 / Lesson 6