9702/May Jun/12/2015/Q7

In an experiment to determine the acceleration of free fall g, a ball bearing is held by an
electromagnet. When the current to the electromagnet is switched off, a clock starts and the ball
bearing falls. After falling a distance h, the ball bearing strikes a switch to stop the clock which
measures the time t of the fall.

If systematic errors cause t and h to be measured incorrectly, which error must cause g to
appear greater than 9.81 m s–2?

A. h measured as being smaller than it actually is and t is measured correctly
B. h measured as being smaller than it actually is and t measured as being larger than it actually is
C. h measured as being larger than it actually is and t measured as being larger than it actually is
D. h is measured correctly and t measured as being smaller than it actually is

Solution:
Answer: D.

Gravitational acceleration (symbolized g) is an expression used in physics to indicate the intensity of a gravitational field. It is expressed in meters per second squared (m/s 2 ).
g = m/s ²

Let h = m, t = s .

Consider choice A:
m decrease , t maintain
the gravitational acceleration appear lesser than 9.81 m/s ²

Consider choice B:
m decrease , t increase
the gravitational acceleration appear lesser than 9.81 m/s ²

Consider choice C:
m increase , t increase
the gravitational acceleration appear lesser than 9.81 m/s ² due to s is power 2.

Consider choice D:
m maintain, t decrease
the gravitational acceleration appear greater than 9.81 m/s ².

Reference: PYQ - May/Jun 2015 Paper 12 Q7