4. What would be the maximum speed, if the haul road were properly maintained with a rolling resistance of 50 pounds per ton

They would have to be hitting each ball with the same force and measuring how far each goes

Explanation: Reviewing the test data that each company has reported on their product is not a bad idea, but each company has a very good reason to want their ball to perform better. Each company may have tested their own balls in the very specific circumstances in which their ball performs better than the competition's. Even if the tests are accurate, they are probably not objective and realistic.

For a scientific test, only one variable should be changed at a time. The variable for this test needs to be the kind of ball, so each ball should be hit with the same force, and the distance the ball travels should be measured. A machine should probably be used to hit the balls to make sure each one is hit with the same force.