1.

A body covers `10 m` in 4 th ` second and ` 15m` in `16 th` second of its uniformly accelerated motion. How far will it travel I the next `3 seconds .

Answer» Here, `D_(4) =10 m , D_(6) =15 ,`
`S_(9) -S _(6)=? `
Let (u) and (a) be the initial velocity and unitorm acceleration of the body. As
`D(n) =u +a/2 (2 n-1)
:. D_(4) +a/2 (2 xx 4-1) =10 ` …(i)
and `D_(6) =u +a/2 (2 xx 6 -1) =15` .. (i)
Subtravting (i) from (iii), we get
`2a=5 or a=(5//2) ms^-2)`
Form (i).,
`u=10 -(5//2)/2 (8-1) =10 -(35)/4 =5/4 ms^(-1)`
Distance travelled in `t seconds is
`S=ut + 1/2 at^(20`
When `t=9s`, then
S_(9) =5/4 xx 1/2 xx 5/2 xx 9^(2) =112. 5 m`
When `t=6 s`,
`S_(6)=5/4 xx 6 +1/2 xx 5/2 xx 6^(2) =52.5 m`
:. Distance travelled in the next three seconds `S_(9 ) S_(6) =112.5 -52 =60.0 m`.


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