12. A student on a distant planet performs a "loop-the-loop" experiment. She releases a frictionless, 1.3 kg cart from a height of 4.50 m. It is observed that the track exerts a downward, normal reaction force of 21 N on the cart at the top of the circle. Calculate the gravitational field strength on the distant planet.* * 4.50 m 1.40 m