Gravitational Potential Energy and Total Energy (Problem 33)

An average-sized asteroid located $5.0\times {10}^7\text{km}$ from Earth with mass $2.0\times {10}^{13}\text{kg}$ is detected headed directly toward Earth with speed of 2.0 km/s. What will its speed be just before it hits our atmosphere? (You may ignore the size of the asteroid.)