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30-Solved-Examples-14

(Physics) > Laws of Motion

Related Practice Questions :

If force on a rocket having exhaust velocity of 300 *m/sec* is 210 *N*, then rate of combustion of the fuel is

(1) 0.7 *kg*/*s*

(2) 1.4 *kg*/*s*

(3) 0.07 *kg*/*s*

(4) 10.7 *kg*/*s*

PMT - 1999

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A 5000 *kg* rocket is set for vertical firing. The exhaust speed is 800 ms^{–1}. 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})** **

(1) 127.5 kg s^{–1}

(2) 187.5 kg s^{–1}

(3) 185.5 kg s^{–1}

(4) 137.5 kg s^{–1}

PMT - 1998

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A rocket has a mass of 100 *kg*. 90% of this is fuel. It ejects fuel vapours at the rate of 1 *kg*/*sec* with a velocity of 500 *m*/*sec* relative to the rocket. It is supposed that the rocket is outside the gravitational field. The initial upthrust on the rocket when it just starts moving upwards is** **

(1) Zero

(2) 500 *N*

(3) 1000 *N*

(4) 2000 *N*

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Rocket engines lift a rocket from the earth surface because hot gas with high velocity** **

(1) Push against the earth

(2) Push against the air

(3) React against the rocket and push it up

(4) Heat up the air which lifts the rocket

AIIMS - 1998

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Sand is being dropped on a conveyor belt at the rate of M kg/s. The force necessary to keep the belt moving with a constant velocity of v m/s will be

(a)Mv newton

(b) 2 Mv newton

(c) $\frac{Mv}{2}$newton

(d) zero

NEET - 2008

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