1) Calculate the force exerted on a rocket, given that the propelling gases are expelled at a rate of 1500 kg/s with a speed of 4.0 x 10^4 m/s (@ the moment of take off)(adsbygoogle = window.adsbygoogle || []).push({}); Answer: 6.0 x 10^7 N

Okay I can not figure how to get an equation to use... Though I did noticed that the rate x the speed in this problem does in fact give you 6.0 x 10^7. Does that play a role?

---

2) A 12,600 kg railroad car travels alone on a level frictionless track with a constant speed of 18 m/s. A 5350 kg load, intially at rest, is dropped on to the car. What will be the car's new speed?Answer: 12.6 m/s

So... here was my approach...

(Before) KE1 + KE2 ( = 0) = (after) KE1 + KE2

(1/2)(12600 kg)((18 m/s)^2) + 0 = (12600 +5350)(v^2)

sq root of 114 = 10.6 m/s... I am off by 2 numbers... did I do something wrong?

---

3) An atomic nucleus intially moving @ 420 m/s emits an alpha particle in the direction of it's velocity, and the remaining nucleus slows to 350 m/s. If the alpha particle has a mass of 4.0 u and the original nucleus has a mass of 222 u what speed does the alpha particle have when it is emitted.Answer: 4.2 x 10^3 m/s

I did the same approach as above with Kinetic energies... Cannot figure out what I am doing wrong. Please help me.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: 3 problems involving linear momentum

**Physics Forums | Science Articles, Homework Help, Discussion**