Posted by joyce on .
a) if a particle's speed decreases by a factor of four, by what factor does its kinetic energy change?
b) particle A has three times the mass and twice the kinetic energy of particle B. What is the speed ratio VA / VB?

physics kinetic energy 
drwls,
a) KE = (1/2) M V^2
What happens to KE when you replace V with a number 4 times larger?
If you can't do that "in your head", try calculating the raio of kinetic energies
KE2/KE1 = (4V)^2/V^2 = ?
b) KEb = KEa/2
KEb/KEa = (Mb/Ma)*(Vb/Va)^2 = 1/2
= (1/3)*(Vb/Va)^2
Solve for Va/Vb