A student uses a trapdoor and electromagnet arrangement to measure the acceleration of free fall. When the electromagnet releases a steel ball, an electronic timer starts. The ball falls through the trapdoor, which breaks an electrical circuit and stops the timer. The student measures the distance fallen as 0.50 m and records a fall time of 0.32 s. Explain why this experimental method can give a reliable measurement of gravitational acceleration, and discuss what sources of error might affect the accuracy of the result.