A student uses a stopwatch with a positive zero error of +0.30\text{ s} to measure the tim… — JAMB UTME

A student uses a stopwatch with a positive zero error of $+0.30\text{ s}$ to measure the time taken for a trolley to travel down an inclined plane. If the stopwatch display reads $15.70\text{ s}$ at the end of the trial, what is the actual time taken by the trolley?

$15.40\text{ s}$ Answer
B
$16.00\text{ s}$
C
$15.70\text{ s}$
D
$15.4\text{ s}$

Answer

The actual time taken by the trolley is

15.40\text{ s}

The correct answer is

15.40\text{ s}

. When a measuring instrument has a positive zero error, it means the scale reads a value greater than zero before measurement begins. Therefore, the true value is found by subtracting the zero error from the observed reading:

15.70\text{ s} - 0.30\text{ s} = 15.40\text{ s}

Step-by-Step Solution

Identify the observed reading and the zero error of the instrument.

Observed reading =

15.70\text{ s}

, Zero error =

+0.30\text{ s}

Instrument readings must be corrected for systematic errors before recording actual values.

Apply the zero error correction formula:

\text{Actual Value} = \text{Observed Reading} - \text{Zero Error}

\text{Actual Time} = 15.70\text{ s} - (+0.30\text{ s}) = 15.40\text{ s}

A positive zero error indicates the timer started above zero, so the initial offset must be subtracted.

Key Concept

Zero Error Correction in Time Measurement Instruments

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