# If the length of a 40 cm spring increases to 64 cm when a 7 kg weight is hanging from it, what is the spring's constant?

Dec 9, 2015

#### Answer:

$166.67 N {m}^{\text{-1}}$

#### Explanation:

you can simply apply the data into the equation $F = k x$
where $F$ is the inner force that occurs inside the string, $k$ is the spring constant and $x$ is the change of length.

nevertheless, according to newton's third law, the inner force that occur inside the spring is equal to the force that is put to it from the outside. which is the weight of the object.

applying the data,
$4 k g \cdot 10 m {s}^{\text{-2}} = k \cdot 0.24 m$
$k = \frac{40}{0.24}$

$k = 166.67 N {m}^{\text{-1}}$