On planet Tehar, the freefall accelration is the same as that on Earth, but there is also a strong downward eletric field that is uniform close to the planet's surface. A 2 kg ball having acharge of 5 micro Coulombs is thrown upward at a speed of 20.1meters per second, and it hits the ground after 4.1 seconds. What is the potential difference between the starting point and the top point of the trajectory?