On planet tehar, the free-fall acceleration is the same as that on earth, but there is also a strong downward electric field that is uniform close to the planet's surface. a 1.84-kg ball having a charge of 5.28 μc is thrown upward at a speed of 20.1 m/s. it hits the ground after an interval of 4.10 s. what is the potential difference between the starting point and the top point of the trajectory? (use 9.8 m/s^2 for the acceleration due to gravity.)