# NCERT Class 9 Science Chapter 7 Work, Energy, and Simple Machines Solutions: In-Text and Exercise Questions Explained | SwaVid

Here are the questions from the new rationalised NCERT Class 9 Science textbook "Exploration", Chapter 7 "Work, Energy, and Simple Machines", along with...

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# Work, Energy, and Simple Machines

## Find the gaps before this chapter finds them for you.

## Related chapters

Chapter 7 · Class 9 Science

Here are the questions from the new rationalised NCERT Class 9 Science textbook "Exploration", Chapter 7 "Work, Energy, and Simple Machines", along with their step-by-step solutions.

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In-text Questions

Answer: The magnitude of the velocity of the child at the bottom of the blue slide will be v = sqrt(2gh), where 'g' is the acceleration due to gravity and 'h' is the vertical height of the slide.

This assumes a frictionless slide and no air resistance.

Revise, Reflect, Refine (NCERT Textbook Page No. 137)

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- Assume the child starts from rest at the top of the slide, so initial kinetic energy (KE_initial) is 0.
- The potential energy at the top (PE_initial) is mgh, where m is the mass of the child, g is the acceleration due to gravity, and h is the vertical height of the slide.
- At the bottom of the slide, the potential energy (PE_final) is 0 (taking the bottom as the reference level).
- The kinetic energy at the bottom (KE_final) is (1/2)mv^2, where v is the velocity at the bottom.
- According to the principle of conservation of mechanical energy (neglecting friction and air resistance), the total mechanical energy at the top equals the total mechanical energy at the bottom: PE_initial + KE_initial = PE_final + KE_final.
- Substitute the values: mgh + 0 = 0 + (1/2)mv^2.
- Simplify the equation: mgh = (1/2)mv^2.
- Cancel out 'm' from both sides: gh = (1/2)v^2.
- Solve for v: v^2 = 2gh, so v = sqrt(2gh).
- The magnitude of velocity depends on the height of the slide and the acceleration due to gravity.
- NCERT Class 9 Science textbook: Exploration : Chapter 7: Work, Energy, and Simple Machines

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