A 10 Kg dog runs at 2m/s. Find its KE

KE = mv²/2 = 10Kg*(2m/s)²/2 = 20Joules

The dog speeds up to 4m/s. Find its KE

KE = 10Kg*(4m/s)²/2 = 80Joules

NOTE: The mass remained the same, the velocity only doubled, yet the KE rose four times!  Notice that "v" is squared in the equation.  This is why car stopping distances become so great at higher speeds.  A car going 60mi/hr has 4X the KE as when it goes 30mi/hr, so it takes four times the distance to stop! Many people think that if you double "v" you only double stopping distance..

If mass doubles and v is held constant, KE doubles.