An asteroid is moving along a straight line. A force acts along the displacement of the asteroid and slows it down. The asteroid has a mass of $5\mathrm{.}3{10}^{4}kg,$ and the force causes its speed to change from $6900$ to $5100\frac{m}{s}.($a$)$ What is the work done by the force? $($b$)$ If the asteroid slows down over a distance of $2\mathrm{.}1{10}^{6}m$ determine the magnitude of the force.