Question

how much does the kinetic energy change is the speed of an object is tripled and its mass is cut in half

Answer 1

Let's take the initial mass of the object = m
velocity = v
initial KE = 1/2 mv² = 0.5mv²

Now the velocity is trippled
V = 3v
mass is cut in half
M = 0.5m
final KE = 1/2 MV² = 1/2 x (0.5m) x (3v)² =9/4 mv² = 2.25 mv²

Change in KE = 2.25mv² - 0.5mv² = 1.75mv²
% change = (Change in KE/initial KE) x 100
                 = (1.25mv²/0.5mv²) x 100
                 = (1.25/0.5) x 100
                 =250%

Change in kinetic energy is 250%

Hope it helps!