Calculating Final Velocity: 1.5kg Cart with 85g Balls vs 255g Ball at 3.5 m/s"

[dishoom]

Momentum Poblem.. Need help!

A 1.5 kg cart is propelled forward by a series of 85g balls being ejected from the rear of the cart with a speed of 3.5 m/s relative to the cart. Calculate the speed of the cart after three balls have been ejected. Compare this to the speed of the cart if it had ejected a signle 255g ball at 3.5 m/s relative to the cart. Assume negligible friction, calculate the final velocity for each cart?

i have got an answer but the relationship is wrong the first cart should have the faster velocity... anyone help i need to understand this!

 

[UrbanXrisis]

A 1.5 kg cart is propelled forward by a series of 85g balls being ejected from the rear of the cart with a speed of 3.5 m/s relative to the cart. Calculate the speed of the cart after three balls have been ejected.

mv=mv
First Ball:
1.415kg(v)=(0.085kg)(3.5m/s)
solve for v then just do the same for second+third

Compare this to the speed of the cart if it had ejected a signle 255g ball at 3.5 m/s relative to the cart. Assume negligible friction, calculate the final velocity for each cart?

mv=mv
1.245kg(v)=(0.255kg)(3.5m/s)
solve for v

 

[dishoom]

umm... that's not it... it's suppose to be relative to the cart.. i know this cause i did something similar to urs and i got it wrong..
and by the way the mass of balls are separate...