# If an object is dropped, how fast will it be moving after 4s?

Apr 16, 2016

$39.2 \frac{m}{s}$

#### Explanation:

If an object is dropped, the major force acting on it is gravity. We mostly ignore smaller variables like air resistance. The acceleration of gravity downwards is about $9.8 m {s}^{-} 2$.

Acceleration is how much velocity ($\frac{m}{s}$) changes by the second, so the units for acceleration are $\frac{\frac{m}{s}}{s}$ or $\frac{m}{s} ^ 2$, which is also written mathematically as $m {s}^{-} 2$.

If we have four seconds of movement, then multiply that by the acceleration and it will give you the velocity.

$9.8 \frac{m}{s} ^ 2 \cdot 4 s = 39.2 \frac{m \cdot s}{s} ^ 2 = 39.2 \frac{m}{s}$