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A body is projected up such that its pos...

A body is projected up such that its position vector varies with time as `r = { 3thati + (4 t - 5t^2)hatj}` m. Here, t is in seconds. Find the time and x-coordinate of particle when its y-coordinate is zero.

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The correct Answer is:
`2.4`
`vec (r) = 3t hat(i) + ( 4 t - 5 t^(2)) hat(j)`
`:. x = 3t` . . . (i)
`y = 4 t - 5 t ^(2)` . . . (ii)
`:.` According to question, ` y = 0 , 4t - 5t^(2) = 0`
`:. t ( 4 - 5 t) = 0 `
`:. t = 0 , or t = (4)/(5) s` ( t = 0 is not accepted)
At ` t = (4)/(5) , x = ( 3 xx 4)/( 5) = (12)/(5) = 2 . 4 m`
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