A model rocket engine has an average thrust of 5.26 N. It has an initial mass of

Question

A model rocket engine has an average thrust of 5.26 N. It has an initial mass of 25.1 9, which includes fuel mass of 12.2 g. The duration of its burn is 1.90 s. (Assume all the fuel is consumed.) (a) What is the average exhaust speed of the engine? m/s (b) This engine is placed in a rocket body of mass 65.0 g. What is the magnitude of the final velocity of the rocket if it were to be fired from rest in outer space by an astronaut on a spacewalk? Assume the fuel burns at a constant rate m/s Need Help? ReadI

Explanation / Answer

Thrust of engine rocket = Force = 5.26 N

a] This thrust is generated by the exhaust gases by buring of fuel.

If V is the average exhaust speed of gases (or engine) and - dm/dt is the rate of buring of fuel mass then thrust F is given by

F = - V dm/dt

= V (m1-m2) /(t2 -t1)

5.26 = V (25.1 - 12.2) * 10^-3 kg / 1.9 sec

V = 5.26 *1.9*1000 / (25.1 - 12.2)

= 774.73 m/s

average speed of the engine

b] The acceleration of rocket is given by

Mr dVr / dt = V [ dm/dt)]

subsript r stands for rocket

it fired from rest Vr(t=0) =0

thrust of engine V*dm/dt = 5.26 N same

Mr = 65 *10^-3 kg and

65*10^-3 [Vr(final) - 0] = 5.26

Vr(final) = 5.26/ (65*10^-3)

= 80.92 m/s answer

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.