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An object starting from rest travels 20 m in first 2 s and 160 m in next 4 s. What will be the velocity after 7 s from the start.

Answers (1)

We can observe that the distance travelled in consecutive seconds is increasing hence we can conclude that object is accelerating.

Let its initial speed is u and acceleration is a.

Hence, by the 2nd equation of motion we can write:

s= ut + \frac{1}{2}at^{2}

20= u(2) + \frac{1}{2}a(2)^{2}

\Rightarrow 20= 2u +2a

\Rightarrow 10= u +a ..................(i)


180 =u (6)+ \frac{1}{2}a(6)^{2}

180 =6u+ 18 a

\Rightarrow 30 =u+ 3 a  ............(ii)

 Solving (i) and (ii)

u = 0

a= 10m /s^{2}

Since, acceleration is same, the velocity after 7 s from the start will be v' = 0+(10\times 7 ) = 70 \;ms^{-1}

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