An object travels North at $7 \frac{m}{s}$ $7 m/s$ for $3 s$ $3 s$ and then travels South at $9 \frac{m}{s}$ $9 m/s$ for $4 s$ $4 s$ . What are the object's average speed and velocity?

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Answer 1 · 2017-01-29T17:16:42

Average speed is $8 \frac{1}{7}$ $8 1/7$ $\frac{m}{s}$ $m/s$ and average velocity is $2 \frac{1}{7}$ $2 1/7$ $\frac{m}{s}$ $m/s$ south.

As the object travels North at $7$ $7$ $\frac{m}{s}$ $m/s$ for $3$ $3$ $s$ $s$ ,

the displacement is $7 \times 3 = 21$ $7xx3=21$ $m$ $m$ north

then the object travels South at $9$ $9$ $\frac{m}{s}$ $m/s$ for $4$ $4$ $s$ $s$ ,

the displacement is $9 \times 4 = 36$ $9xx4=36$ $m$ $m$ south

Hence, net displacement is $36 - 21 = 15$ $36-21=15$ $m$ $m$ south in $3 + 4 = 7$ $3+4=7$ $s$ $s$

As total distance covered is $21 + 36 = 57$ $21+36=57$ $m$ $m$ in $7$ $7$ seconds,

average speed is $\frac{57}{7} = 8 \frac{1}{7}$ $57/7=8 1/7$ $\frac{m}{s}$ $m/s$

But average velocity is $\frac{15}{7} = 2 \frac{1}{7}$ $15/7=2 1/7$ $\frac{m}{s}$ $m/s$ south.

An object travels North at 7ms7 m/s for 3s3 s and then travels South at 9ms9 m/s for 4s 4 s. What are the object's average speed and velocity?