Physic C..........help <span title="me.......seriously!!!!!!!?">me.......seriously!!!!!!!...</span>

Question

A rocket sled with a mass of 2900 kg moves at 250 m/s on a set of rails. At a certain point, a scoop on the sled dips into a trough of water located between the tracks and scoops water into an empty tank on the sled. By applying the principle of conservation of linear momentum, determine the speed of the sled after 920 kg of water has been scooped up. Ignore any retarding force on the scoop.

Answer 1

Always begin by writing out the equations you might need.  The problem states linear momentum may be the key, so initial momentum equals final momentum if momentum it is conserved (and you were told it was). In other words:

m1*v1=m2*v2.  (momentum is just mass * velocity)

Next write what variables you know.  You know m1=2900 kg and v1= 250 m/s.  You also can quickly figure that m2=920 kg + m1 (it scoops up water, changing the mass and ultimately the velocity to conserve momentum.  You have 1 equation with 1 unknown (v2), which can always be solved when the number of unknowns matches the number of equations you hae to solve (e.g, if you have 2 equations and 2 unknowns you are stil in good shape).  Solve the equation for v2 and you are done.  I will let you do that, and I am sure you will get the right answer.  Follow these general steps and physics is easy; just plow ahead with what you know and list what is given and figure out how to solve for the unknown variables.   Good luck.

Answer 2

V2 = V1*(M1/(M1+M2)) = 189.8 m/s