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Basic Mechanics Question Paper

Basic Mechanics

Course:Bachelor Of Electrical And Electronics Engineering

Institution: Moi University question papers

Exam Year:2011

BASIC MECHANICS

1. The engine of a missile ejects 100 kg of exhaust gases per second at a speed of 800 m/s relative to the engine. Calculate the thrust of the engine at a forward speed of 200 m/s:
a. When the missile is rocket-propelled;
b. When jet propelled.
What is the power developed when jet propelled?

2. A rocket engine has a thrust of 1.2 MN at lift-off. If its specific impulse is 2.5 kN s/kg, what is the rate of consumption of propellant?

3. A rocket of total mass 100 tonnes is to leave its launching pad vertically with an acceleration of 2 metres per square seconds. If the velocity of the burnt gases leaving the pocket is limited to a speed of 3 km/s relative to the rocket, find the mass flow rate of gas to give the initial acceleration.

4. A communications satellite of mass 220 kg is orbiting at 10500 m/s when its retro-pockets are fired for 8 s to reduce its speed to 10475 m/s. Find the rate of discharge of exhaust gases required from the rocket to produce the necessary thrust if the speed of the exhaust jet relative to the satellite is to be 550 m/s. Assume the only force acting on the satellite to be the thrust of the rockets.

5. A single stage rocket has a total initial mass of 4000 kg, including 2800 kg of propellant which is used up in 70 s in vertical flight. The exhaus jet velocity is 1.4 km/s relative to the rocket. Allowing for the loss of mass of propellant, estimate the acceleration at the instant of burn-out. What is the specific impulse of the rocket? If the total mass is actually 1 percent greater than the given value, what is the percentage error in calculating the acceleration at burn out?

6. A rocket of mass 250 t is launched vertically and hovers just above the pad. The mass flow rate of propellant is 845 kg/s. Find the specific impulse at this instant.

7. A rocket has a lift-off weight of 8.8 kN and the propellant accounts for 60 percent of this weight. Vertical lift-off with negligible resistance occurs when the initial thrust exceeds the dead weight by 18 percent. The exhaust jet velocity relative to the rocket is limited to 1.1 km/s. Find the burning time and the acceleration al lift-off.

8. An 80 kg satellite is in orbit in steady flight when its control rockets burn for 3 s, issuing a jet at at 200 m/s relative to the satellite, backwards in the line of flight. The satellite''s speed increases by 6 m/s. Find the additional distance travelled during the burn and the mass flow rate of propellant.

Basic Mechanics Question Paper

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