Kinematics Equation

Question

A body moving with uniform acceleration in a straight line travels 20m in the first second and 40m in the next second. How far will it travel in the third second of its motion?

Answer 1

If the acceleration is constant your position function is:

$$s(t)=s(0)+v_0t+\frac{at^2}{2}$$

For this question you can suppose $s(0)=0$ then we have $$s(1)=20=v_0+\frac{a}{2}\quad (1)$$ and $$s(2)=20+40=60=2v_0+2a\quad (2)$$

Form $(1)$ and $(2)$, find $v_0$ and $a$ and then calculate $s(3)-s(2)$.

Can you finish?