1.2.7 | до правки #12869 | Решения Савченко

Statement

1.2.7. The bus moves for $$20$$ seconds in a straight line to the stop, passing a distance of $310 \text{ m}$ . Its initial speed is $15~\mathrm{\frac{m}{s}}$ . Prove that the velocity of the bus changes in direction.

Solution

Since the bus comes to a complete stop at the end, the average speed is
test
$v_\text{average}=\frac{15+0}{2}~ \mathrm{\frac{m}{s}}=7.5~ \mathrm{\frac{m}{s}}$

If there is an equal-accelerated motion, then the body must travel a path

$s = v_\text{average}\cdot t=150\text{ m}$

Whence it follows that the body has accelerated, but the motion is not equal-accelerated

Answer

The average velocity is greater than the initial velocity and the final velocity is zero.