We can use the formula:
v = u + at
where:
v = final velocity = 70 m/s
u = initial velocity = 0 m/s (since the roller coaster starts from rest)
a = acceleration = 8.75 m/s²
t = time
Solving for t, we get:
t = (v - u) / a
t = (70 m/s - 0 m/s) / 8.75 m/s²
t = 8 seconds
Therefore, it takes 8 seconds for the roller coaster to speed up.