- #1

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I'm not sure if the first part is correct, I just need some feedback on that.

Also I'm not sure how to calculate velocity or altitude after 1 second.

Any help would be awesome!

## Homework Statement

A rocket has an initial mass of 4000kg, of which 3000kg is fuel. Total burn time after launch is 8 seconds. Exhaust velocity is 400m/s. The rocket lifts off vertically.

(a) Evaluate “Thrust”, V(dM / dt)

(b) Using Newton’s second law, evaluate acceleration of the rocket after 1 second of flight.

(c) Calculate the rocket’s velocity after 1 second.

(d) Calculate the altitude reached after 1 second.

(e) Calculate the kinetic energy ½ (Mv2) of the rocket after 1 second.

(f) Calculate the gravitational potential mgh of the rocket after 1 second.

## Homework Equations

g = 10m/s2

(Thrust / recoil Mass) gives acceleration

Evaluate “Thrust”, V(dM / dt)

## The Attempt at a Solution

(a) Evaluate “Thrust”, V(dM / dt)

3000/8 = 375kg/s of fuel each seconds

**Table -**

**Time(t):**0....1...2...3

**Mass(M):**4000...3625...3250...2875

**Thrust:**.....75,000

**A:**...18.75...20.69...23.08

Thrust = 400 * (375/2) = 75,000N

(b) Using Newton’s second law, evaluate acceleration of the rocket after 1 second of flight.

(Thrust / recoil Mass) gives acceleration

A = 75,000 / 3625

Acceleration: 20.69m/s2

(c) Calculate the rocket’s velocity after 1 second.

Time(t): 0 1 2

A: 18.75 20.69 23.08

(d) Calculate the altitude reached after 1 second.

(e) Calculate the kinetic energy ½ (Mv2) of the rocket after 1 second.

(f) Calculate the gravitational potential mgh of the rocket after 1 second.