How long does it take for a car, moving with an acceleration of 0.4 m / s2, to increase its speed from 12 to 20 m / s?

How long does it take for a car, moving with an acceleration of 0.4 m / s2, to increase its speed from 12 to 20 m / s? The sled rolled down the 60 m long mountain in 10 seconds. With what acceleration did they move?

First task.
Given:
a = 0.4 m / s;
V1 = 12 m / s;
V2 = 20 m / s.
Find: delta t.
Decision:
This formula should be applied:
V2 = V1 + a * delta t.
Next, we express the delta t from it.
Delta t = (V2-V1) / a.
We substitute known values ​​into the formula and find the answer.
Delta t = (20-12) / 0.4 = 8 / 0.4 = 20 s.
Answer: delta t = 20 s.

Second task.
Given:
S = 60 m;
t = 10 s;
V initial = 0 m / s.
Find: a.
Decision:
We use this formula:
s = Vinitial * t + at ^ 2/2.
Let us express the acceleration a from it.
V initial * t can be removed, since it will be equal to zero.
s = at ^ 2/2
2s = at ^ 2
Let’s plug in the values ​​we know to find the answer.
a = 2s / t ^ 2 = 2 * 60/10 ^ 2 = 120/100 = 1.2 m / s ^ 2.
Answer: a = 1.2 m / s ^ 2.