Measuring free fall with electronic timing

Part (a) marking points

Final answer: 0.0605 s². Numerical checks assess the final value only; they do not check working or the number of digits typed.

1. Square 0.246 s. (1 method mark)
2. Obtain 0.0605 s². (1 accuracy mark)

No earlier numerical result is required. Award method credit for valid working and accuracy credit for the stated answer. Accept a defensible equivalent method; wrong physics cannot earn dependent accuracy credit.

Common errors: This is t rather than t squared.

Part (b) marking points

Final answer: 9.80 m s⁻². Numerical checks assess the final value only; they do not check working or the number of digits typed.

1. Gradient is (0.491 − 0.099)/(0.100 − 0.020) = 4.90 m s⁻². (1 method mark)
2. Use g = twice the gradient = 9.80 m s⁻². (1 accuracy mark)

No earlier numerical result is required. Award method credit for valid working and accuracy credit for the stated answer. Accept a defensible equivalent method; wrong physics cannot earn dependent accuracy credit.

Common errors: The h–t² gradient is g/2, not g.

Part (c) marking points

1. Reaction-time variation is large relative to the short fall times. (1 independent mark)
2. Electronic timing avoids manual start/stop reaction delays and their large relative uncertainty. (1 independent mark)

Award each distinct physical point once. Equivalent scientifically correct wording is creditable; a contradictory statement cannot earn the same point.

Part (d) marking points

1. Recorded times are systematically too long. (1 independent mark)
2. Calculating g = 2h/t² from an individual drop then gives a value too low. (1 independent mark)
3. Repeating and averaging does not remove the fixed delay. (1 independent mark)

Award each distinct physical point once. Equivalent scientifically correct wording is creditable; a contradictory statement cannot earn the same point.