# 1002 Location of warning torpedo | Rectilinear Translation

**Problem 1002**

On a certain stretch of track, trains run at 60 mph (96.56 kph). How far back of a stopped train should be a warning torpedo be placed to signal an oncoming train? Assume that the brakes are applied at once and retard the train at the uniform rate of 2 ft/sec^{2} (0.61 m/s^{2}).

**Solution**

English System
Initial velocity

$v_i = 60 \, \text{ mph} = 60(\frac{22}{15})$
Initial velocity

$v_i = 96.56 \, \text{ kph} = 96.56(\frac{1}{3.6})$

$v_i = 60 \, \text{ mph} = 60(\frac{22}{15})$

$v_i = 88 \, \text{ ft/sec}$

${v_f}^2 = {v_i}^2 + 2as$

$0^2 = 88^2 - 2(2)s$

$s = 1936 \, \text{ ft}$ *answer*

SI units

$v_i = 96.56 \, \text{ kph} = 96.56(\frac{1}{3.6})$

$v_i = 26.82 \, \text{ m/sec}$

${v_f}^2 = {v_i}^2 + 2as$

$0^2 = 26.82^2 - 2(0.61)s$

$s = 589.7 \, \text{ m}$ *answer*

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