5.1.5 Rocket Propulsion

Question 1

Rocket Propulsion

Answer 1

• Throwing objects from a rocket in deep space will cause the rocket to accelerate in the opposite direction.
• The rocket equation, , relates the force on a rocket to its thrust.
• Integration of the rocket equation results in , which relates the rocket’s final velocity to the velocity of the exhaust and the rocket’s initial and final mass.

Question 2

A rocket fires its engines for 2 s, which decreases the mass by 1%. The burned fuel is ejected with an exhaust speed of 2,000 m / s. Which of the following is the acceleration?

Answer 2

10 m / s2

Question 3

The launch vehicle for something as large as the space shuttle can consume up to 600,000 kg / min of fuel and eject the burned fuel at speeds of 4 km / s. How much thrust do these rockets produce?

Answer 3

4 × 10^7 N

Question 4

A rocket starts off at rest and has 1/4 of its initial mass as fuel. If all the fuel is burned up in 90 s, and the exhaust velocity is 2,400 m / s, what is the final speed of the rocket?

Answer 4

690.4 m / s

Question 5

A rocket is fired in deep space and in the first second ejects 1/160 of it total mass as exhaust gas. If it has an acceleration of 15 m / s2, what is the speed of the exhaust gas relative to the rocket?

Answer 5

2,400 m / s

Question 6

A spaceship is at rest in deep space. It fires its rocket so that in 1 s 1/120 of its mass is ejected with an exhaust speed of 2,400 m / s. Which of the following is the spaceship’s initial acceleration?

Answer 6

+20 m / s2

Question 7

The initial mass of a rocket and its fuel is 6,000 kg. Its exhaust velocity is 2,000 m / s. How much gas must be ejected in the first second of burning to have an acceleration of 25 m / s2?

Answer 7

75 kg

Question 8

A rocket is fired from rest in deep space. If all of its fuel is burned in 50 s, and the relative exhaust speed is 2,100 m / s, what must the mass ratio mo  /  mf  be for a final speed of 8,000 m / s?

Answer 8

45.2

Question 9

Rocket A’s mass is 70% fuel and 30% payload. Rocket B’s mass is 90% fuel and 10% payload. If both start from rest, how many times faster must Rocket A’s exhaust speed be in order to end up with the same final velocity as the Rocket B after all of both rockets’ fuel is burned?

Answer 9

1.9

Question 10

Evaluate the following as true or false. The proper equation for the conservation of momentum for a rocket that starts off with some velocity, v, and then fires its engines is mv = (m+delta m)(v+delta v) a= (-delta m)(v - vex)

Answer 10

true