An object travels North at $7 m/s$ for $5 s$ and then travels South at $9 m/s$ for $2 s$ . What are the object's average speed and velocity?

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Answer 1 · 2016-05-13T14:38:13

$vecV_"net"=2.43m/s->"towards north"$

$V_"avg" ~~7.6m/s$

For 1st 5s the velocity of the object towards North be
$vecV_"north"=7hatjm/s$

For 1st 5s the displacement of the object towards North be
$vecd_"north"=7hatjm/sxx5s=35hatjm$

For 2nd 2s the velocity of the object towards Southbe $vecV_"south"=-9hatjm/s$

For 2nd 2s the displacement of the object towards Southbe $vecd_"south"=-9hatjm/sxx2s=-18hatjm$

Net displacement during t=(5+2)=7s is
$vecd_"net"=35hatjm-18hatjm=17hatjm->"towards north"$

Hence the Net Velocity
$vecV_"net"=vecd_"net"/t=17/7hatjm=2.43m/s->"towards north"$

Total distance covered during 7 s
$d_"total"=|vecd_"north"|+|vecd_"south"|=|35hatjm|+|-18hatjm|=53m$

Hence Average speed
$V_"avg" = d_"total"/t=53/7m/s~~7.6m/s$

An object travels North at 7 m/s7 m/s for 5 s5 s and then travels South at 9 m/s9 m/s for 2 s 2 s. What are the object's average speed and velocity?