In physics, it is already convenient since there are already derivedequations for rectilinear motions with constant acceleration. These equations are all derived from Newton's Laws of Motion.
2ax = vf^2 -v0^2
x = v0*t + 1/2*a*t^2
where
a is the acceleration in m/s^2
vf is the final velocity in meters
v0 is the initial velocity in meters
x is the distance travelled in meters and,
t is the time in seconds
a.) For this case, you'll find x when t=2 s. Using the second equation,
x = v0*t + 1/2*a*t^2
x = 15*2 + 1/2*4*2^2
x = 38 m
b.) For this case, you'll find x when vf is 25 m/s. Using the first equation,
2ax = vf^2 -v0^2
2*4*x = 25^2 -15^2
x = 50 m
