volume_mute

A man drops a 10-kg rock from the top of a 5-meter ladder

publish date: 2023/07/24 00:34:00 GMT+10

volume_mute

Assuming that air friction is negligible, how much kinetic energy does it have when it hits the ground?  Calculate the answer yourself if you can.

Hint: First Calculate the potential energy at the top

Potential energy at top = weight • height

Remember weight = mass • gravity = mg

PE = mg • height

  1. PE = kg • m/s2 • m
  2. PE = (kg • m/s2) • m
  3. PE = newton • m
  4. PE = joules

What is the speed of the rock just before it hits the ground (approximate your answer)? m/s

Correct Answer

(1) 10
(2) 9.8
(3) 5
(4) 490
(5) 490
(6) 490
(7) 10

Explanation

A detailed answer regarding the speed of the rock

10 m/s (Since we are assuming that no energy was lost to frictional forces, the potential energy at the top is equal to the kinetic energy at the bottom.)

KE = \(\frac12mv^2\)

490 = \(\frac12 \cdot 10 \cdot v^2\)

v2 = 98

v ≅ 10 m/s

≅ means "approximately equal to"

Reference

Basic Physics: A Self-Teaching Guide

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