# [SOLVED] Help with basic physics problem on kinetic energy?

Help with basic physics problem on kinetic energy?

A mother has four times the mass of her young son. Both are running with the same kinetic energy.

What is the ratio [vs/vm] other of their speeds?

Express your answer using two significant figures.

The Best answer for Help with basic physics problem on kinetic energy?

mass of mother = 4 mass of sun

mothers KE

0.5( 4 m) vm^2

sons KE

0.5( m) vs^2

their KE are equal

0.5( 4 m) vm^2 = 0.5( m) vs^2

solve for vs / vm

vs^2/ vm^2 = 4

vs/vm = sqrt 4

vs/vm =2.0

If you consider the sons mass as m then the mothers mass is 4m. KE=1/2 mv^2. so moms kinetic energy is 2MVm^2 and sons is 1/2MVs^2.They are equal so Vs^2/Vm^2=4

Vs/Vm=2 thus the ratio is 2:1 that is 2.0

i think this is the correct answer Help with basic physics problem on kinetic energy?

55mile/h = fifty 5 *1609.3/3600 m/s = 24.586 m/s 67mile/h = sixty seven*1609.3/3600 m/s = 29.ninety 5 m/s W = a million/2 * m * (v^2 – u^2)=a million/2 * m * (29.ninety 5^2 – 24.586^2) F * S = a million/2 * m * (897 – 604.5) m * g * S = a million/2 * m * 292.5 S = 146.25/10 = 14.625 m