Question

Qual a energia cinética de uma partícula de massa de 5kg cuja velocidade vale 72km/h

Answer 1

72/3,6 = 20 m/s

Ec = mv²/2
= 5 . 20²/2
= 1000 J

Answer 2

$m = 5\,kg \\ v = 72\,km\!/\!h = 20\,m\!/\!s \\ \\ E_c = \frac{m.v^2}{2} \\ \\ E_c = \frac{5.20^2}{2} \\ \\ E_c = \frac{5.\,4.10^2}{2} \\ \\ E_c = \frac{2.10^3}{2} \\ \\ E_c = 1.10^3\,J$