Question

A boy begins to walk eastward along a street In front of his house, and the graph of his displacement from home is shown in the following figure. His average velocity for the whole time interval is equal to:

• A. $8\, m/min$
• B. $6\, m/min$
• C. $\frac{8}{3}\, m/min$
• D. $2 \, m/min$

Answer 1

Answer: (D)

$2 \, m/min$

Answer 2

Key Idea : The average velocity is defined as total displacement of the body in a particular time interval divided by the time interval.
Displacement from $0$ to $5\, s =40 \,m$
Displacement from $5$ to $10 \,s =40 \,m$
Displacement from $0$ to $15\, s =-20 \,m$
and displacement from $15$ to $20\, s =0\, m$
$\therefore$ Net displacement
$=40+40-20+0=60\, m$
Total time taken $= 5 + 5 + 1 5 + 5 =30\, min$
Hence, average velocity $=\frac{\text { displacement }( m )}{\text { time }( min )}$
$=\frac{60}{30}=2\, m / min$