On planet Tehar, the free-fall acceleration is the same as that on Earth, however there is also a strong downward electric field that is uniform close to the planet's surface. A 2.02 kg ball having a charge of 5.01 µC is thrown upward at a speed of 20.1m/s. It hits the ground after an interval of 4.10 s. What is the potential difference among the starting point and the top point of the trajectory? (Answer in kv)