159 6. What will be cost in rupees of 3 - kg of twine at Rs. 1.10 per kg and 20 envelopes at Re. 0.60 per dozen ? (A) Rs. 4.80 (B) Rs. 4.85 (C) Rs. 4.90 (D) Rs. 5​

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Aspacecraft can attain a stable orbit 300 kilometers above earth if it reaches a velocity of 7.7 kilometers per second. the formula for a rocket's maximum velocity v in kilometers per second is vequalsminus0.0098tplusc ln upper r, where t is the firing time in seconds, c is the velocity of the exhaust in kilometers per second, and r is the ratio of the mass of the rocket filled with fuel to the mass of the rocket without fuel. find the velocity of a spacecraft whose booster rocket has a mass ratio of 20, an exhaust velocity of 2.1 km/s, and a firing time of 15 s. can the spacecraft achieve a stable orbit 300 km above earth?

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