An object travels North at $6 \frac{m}{s}$ $6 m/s$ for $9 s$ $9 s$ and then travels South at $6 \frac{m}{s}$ $6 m/s$ for $7 s$ $7 s$ . What are the object's average speed and velocity?

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Answer 1 · 2017-02-20T16:24:39

The average speed is 6m/s; the average velocity is 0.75 m/s North.

First, we must determine the displacement of the object during each time interval.

During the first 9s

$d = v \times t = 6 \frac{m}{s} \times 9 s = 54 m$ $d=vxxt = 6m/sxx9s = 54m$ North

During the next 7s

$d = v \times t = 6 \frac{m}{s} \times 7 s = 42 m$ $d=vxxt = 6m/sxx7s = 42m$ South

For the average speed , we consider only the total distance travelled and the total time taken

$v_{ave} = d \div t = 96 m \div 16 s = 6 \frac{m}{s}$ $v_"ave" = d-:t = 96 m-:16 s = 6 m/s$

For the average velocity , we consider the net displacement and the time taken. The net displacement has been only 12 m North.

${\to v}_{ave} = \to d \div t = 12 m N \div 16 s = 0.75 \frac{m}{s}$ $vecv_"ave"=vecd -:t = 12m N -: 16s = 0.75 m/s$ North

An object travels North at 6 m/s6ms6 m/s for 9 s9s9 s and then travels South at 6 m/s6ms6 m/s for 7 s7s7 s. What are the object's average speed and velocity?