Problem 2-98 - Linear Kinematics - Part 5 - (b)

 A helicopter is traveling horizontally, straight toward a cliff. When \(700 \;m\) from the cliff, it sends a sonar signal and \(3.4\; s\) later receives the reflected signal. Assuming the signal travels at \(350 \;m/s\), determine the speed of the helicopter.

diagram of helicopter

Accumulated Solution

\(d = vt \\ d = (350\; m/s)(3.4\; s) = 1190\; m \\ \text{The helicopter encounters the echo} \; 1190 - 700 = 490\; m\; \text{ from the cliff.}\)

Correct.

diagram of helicopter flying

The helicopter has traveled \(700 - 490 = 210\; m \; \text{in} \; 3.4 \;s.\)

What is the speed of the helicopter?

(A)   \(\text{speed} = d/t = 210\; m/3.4\; s = 62 \;m/s\)

(B)   \(\text{speed} = d/t = 700 \;m/3.4\; s = 206\; m/s\)

(C)   \(\text{speed} = d/t = 490\; m/3.4\; s = 144 \;m/s\)