In a baseball game the batter hits the ball into center field and takes off for first base. the catcher can only stand and watch. assume that the batter runs at a constant velocity. who measures the proper time it takes for the runner to reach first base, and who measures the proper length between home plate and first base? the runner measures both the proper time and the proper length. the catcher measures both the proper time and the proper length. the runner measures the proper time, and the catcher measures the proper length. the catcher measures the proper time, and the runner measures the proper length.

Thus, The statement " the runner measures the proper time and the catcher measures the proper length" is a correct statement.

Explanation:

Proper time interval Δt is the time interval between two events as measure of by the observer who rest with respect to events and views them at the time occurence.

The beginning of the event is the start of the run to first base. The end of event is the finish of the run to first a base. Since the runner with constant velocity, he sees the beginning and the end of the event occur next to him so that the event seems to take place at the same place. He is also at rest relative to his clock. Hence, the runner measures the proper time interval.

The proper length L_0 between two points is the length measured by the observer who is at rest relative to the points.

The catcher is at rest relative to the distance from home plate and first base and hence measures the proper length.

Thus, The statement " the runner measures the proper time and the catcher measures the proper length" is a correct statement.