A model rocket sits on the launch pad until its fuel is ignited, blasting the rocket upward. During the short time of blast-off, as the ignited fuel goes down, the rocket goes up because:
a. the fuel pushes on the ground.
b. air friction pushes on the escaping fuel.
c. the downward force of gravity is less than the downward momentum of the fuel.
d. of none of the above reasons.
[Ques. 2] A helicopter stays aloft by pushing large quantities of air downward every second. What mass of air must be pushed downward at 35.0 m/s every second to keep a 1 500-kg helicopter aloft?
a. 42.9 kg
b. 420 kg
c. 430 kg
d. 410 kg
e. 415 kg
[Ques. 3] A 1 500-kg experimental rocket sled at rest on level frictionless rails is loaded with 55.0 kg of propellant. It exhausts the propellant in a 20-s burn. The rocket moves at 155 m/s after the burn. What average force is experienced by the rocket during the burn?
a. 4.26E+2 N
b. 1.16E+4 N
c. 1.21E+4 N
d. 1.94E+2 N
e. 2.33E+5 N
[Ques. 4] A 1 200-kg experimental rocket sled on level frictionless rails is loaded with 55.0 kg of propellant. It exhausts the propellant in a 20-s burn. If the rocket, initially at rest, moves at 155 m/s after the burn, what impulse is experienced by the rocket sled?
a. 8.5E+3 kg/m/s
b. 1.3E+5 kg/m/s
c. 1.9E+5 kg/m/s
d. 8.5E+5 kg/m/s
e. 2.1E+5 kg/m/s
[Ques. 5] A model car is propelled by a cylinder of carbon dioxide gas. The cylinder emits gas at a rate of 5.00 g/s with an exit speed of 80.0 m/s. The car has a mass of 455 g, including the CO2 cylinder. Starting from rest, what is the car's initial acceleration?
a. 0.879 m/s2
b. 40.0 m/s2
c. 36.4 m/s2
d. 7.28 m/s2
e. 1.38 m/s2
[Ques. 6] Neglecting gravity, doubling the exhaust velocity from a single stage rocket initially at rest changes the final velocity attainable by what factor? Assume all other variables, such as the mass of the rocket and the mass of the fuel, do not change.
a. The final velocity stays the same.
b. The final velocity doubles.
c. The final velocity increases by a factor of 0.693.
d. The final velocity increases by a factor of 0.310.
[Ques. 7] A rocket with initial mass of 3.0 104 kg fires its engines at t = 0 . The exhaust speed of the rocket is 3.9 103 m/s. If the velocity of the rocket at t = 200 s is 1 500 m/s, how much fuel did it consume?
a. 9.6 103 kg
b. 3.0 104 kg
c. 4.4 104 kg
d. 4.8 103 kg
[Ques. 8] A satellite engine has an exhaust speed of 2.80 104 m/s and ejects ionized gas at a rate of 2.50 106 kg/s. What is the instantaneous thrust of the engine?
a. 8.93 1011 N
b. 7.00 102 N
c. 5.30 102 N
d. 1.12 1010 N
[Ques. 9] A rocket has an exhaust speed of 2.5 103 m/s, and produces 7.5 105 N of instantaneous thrust. What mass of fuel does the rocket burn each second?
a. 3.30 103 kg/s
b. 17.1 kg/s
c. 300 kg/s
d. 1.90 109 kg/s
[Ques. 10] A 2 500-kg car moving north collides with a 2 000-kg car moving west. After the collision, the cars stick together and move at an angle of 45 north of west at a speed of 8.0 m/s. What was the initial speed of the 2 500-kg car?
a. 20 m/s
b. 10.2 m/s
c. 14 m/s
d. 9.3 m/s
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