A 500kg rocket is set for verticle firing. The exhaust speed is 800`ms^-2` . To give an initial upward acceleration of 20`ms^-2` , the amount of gas ejected per second to supply the needed thrust will be (g=10 `ms^-2` )

Options

A. `127.5 kg//s`
B. `187.5 kg//s`
C. `85 kg//s`
D. `137.5 kg//s`

Answer

B

Explanation

`Ma = v_(r ) (dm)/(dt)`
`v_( r) (dM)/(dt) = M(a + g)`
`(800) (dM)/(dt) = 5000 (20 + 10)`
`(dM)/(dt) = 187.5 kg//s`