8.2 Exercise 11

A particle of mass $2.0 \text{kg}$ moves under the influence of the force $F \left(x\right) = \left(−5 x^{2} + 7 x\right) \text{N} .$ If its speed at $x = −4.0 \text{m}$ is $v = 20.0 \text{m}/\text{s},$ what is its speed at $x = 4.0 \text{m} ?$