# 1) At the highest point kinetic energy is minimum/maximum while the potential energy is...

## Question:

1) At the highest point kinetic energy is minimum/maximum while the potential energy is minimum/maximum.

2) At the lowest point kinetic energy is minimum/maximum while the potential energy is minimum/maximum

3) Mass affects/ does not affect the conservation of energy

4) A 75kg skater starts his skate with an initial speed of 0.0 m/s, 8.0m above the ground. Just before he reaches the ground, all the potential energy became kinetic energy. How much work was done by gravity

## Energy conservation in projectile motion:

When an object is thrown upward on the earth's surface, its motion is called projectile motion. Energy is conserved during such motion. Kinetic energy is converted into potential energy and potential into kinetic such that the sum total of kinetic energy and potential energy remains constant throughout the motion. Work done by gravity when an object of mass 'm' falls from a height 'h' is given by:

{eq}mgh {/eq}, where g is the acceleration due to gravity. {eq}g = 9.81 \frac{m}{s^2} {/eq}

## Answer and Explanation:

At the lowest point, the object is thrown upward with some speed. Its speed keeps decreasing till it reaches the highest point. At the highest point, the object stops momentarily, hence its speed is zero at the highest point. The speed is maximum at the lowest point.

1) At the highest point, speed is zero and so the kinetic energy is minimum(zero) while the potential energy is maximum.

2) At the lowest point, the speed is maximum and so the kinetic energy is maximum while the potential energy is minimum.

3) Energy can neither be created nor be destroyed. It only changes from one form to another. It is always conserved. hence the mass doesn't affect the conservation of energy.

4) Work-done by gravity = Force of gravity x displacement

{eq}= mg \times h =75kg * 9.81 * 8m = 5886 J {/eq}

#### Learn more about this topic: What is Energy Conservation? - Definition, Process & Examples

from ICSE Environmental Science: Study Guide & Syllabus

Chapter 1 / Lesson 6
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