Speed of Falling

Classical Mechanics Level 2

Person A jumps off a 500 m tower, his mass is 80 kg, and the gravitation field strength is 9.8m/s^2 on earth. Assuming that 80% is usefully transferred to kinetic energy, what would his speed be when falling down? Answer to the nearest integer in m/s.


The answer is 89.

Himeth Hollu by himeth hollu , 16, United Kingdom

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2 solutions

Tom Engelsman
Apr 28, 2019

We require 0.8 m g h = 1 2 m v 2 ⇒ v = 1.6 g h = 1.6 ⋅ 9.8 ⋅ 500 = 88.54 0.8mgh = \frac{1}{2}mv^2 \Rightarrow v = \sqrt{1.6gh} = \sqrt{1.6 \cdot 9.8 \cdot 500} = \boxed{88.54} m/s.

2 Helpful 1 Interesting 1 Brilliant 0 Confused
Himeth Hollu
Apr 29, 2019

Equation for GPE= mass * gravitation field strength * height

80 * 9.8 * 500 = 392000

Equation for genetic energy = 0.5 * mass * velocity^2

Rearranged equation for velocity = sqrt(2*KE/mass)

Usefully transferred energy = 392000 * 0.8 = 313600

v = sqrt(2*313600/80)

v= sqrt(7840)

v= 88.54

v= 89 m/s

0 Helpful 0 Interesting 0 Brilliant 0 Confused

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