Lets Cross The Axis

Classical Mechanics Level 2

An object moves in two dimensions according to

$\vec{r}(t) = (4.0t^2 - 9.0)\vec{i} + (2.0t - 5.0)\vec{j}$

where $r$ is in meters and $t$ in seconds. When does the object cross the $x$ -axis?

0.4 s

0.0 s

1.5 s

0.6 s

2.5 s

1 solution

Danish Ahmed
Nov 22, 2015

The object crosses the $x$ -axis when the $y$ coordinate is $0$ , or when $2t-5=0$ . The answer is $\boxed{2.5}$ .

The shortest precise solution. Very good.

Muhammad Arifur Rahman - 5 years, 6 months ago