- #1

AnhTran

- 2

- 0

## Homework Statement

The payload of a spaceship accounts for 20% of its total mass. The ship is traveling in a straight line at 2100km/hr relative to some inertial observer O. When the time is right, the spaceship ejects the payload, which is moving away from the ship at 500km/hr immediately after the ejection. How fast is the spaceship now moving, as observed by O

## Homework Equations

total momentum before launch equal total momentum after launch

p=mv

v(p)=v(p/s)+v(s) (relative velocity of the payload after launch)

m(s): mass of the body of the ship

m(p): mass of the payload

v(si): velocity of the body of the ship before launch

v(pi): velocity of the payload before launch

v(sf): velocity of the body of the ship after launch

v(pf): velocity of the body of the ship after launch

## The Attempt at a Solution

since the total mass is not given, I let the mass of the body of the ship equal 1 and the mass of the payload equal 0.25

my equation: m(s)*v(si)+m(p)*v(pi)=m(s)*v(sf)+m(p)*v(pf)

substituting for the variable: 1(2100)+0.25(2100)=1(2100-v(s))+0.25(500+v(s))

v(s) equal -533.33km/hr, which is greater than 500, which shows that the actual velocity of the payload is opposite of velocity of the entire ship before launch. I don't know how I did it wrong so if someone can help me on this I will be very grateful.