The ball is projected up from ground with speed $$30\,m/\sec .$$ What is the average velocity for time 0 to $$4\,\sec $$ ?
A.
$$10\,m/\sec $$
B.
$$20\,m/\sec $$
C.
$$15\,m/\sec $$
D.
zero
Answer :
$$10\,m/\sec $$
Solution :
We should know the displacement in this time.
$$\eqalign{
& \overrightarrow S = \overrightarrow u t + \frac{{\overrightarrow a {t^2}}}{2}\,\left( {{\text{we take upward as positive}}} \right) \cr
& S = 30 \times 4 - 10 \times 4 \times \frac{4}{2} = 40\,m. \cr} $$
The average velocity will be $$10\,m/\sec .$$
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