Velocity due to increasing mass

[fondrika]

Homework Statement

if a 50kg car has a static speed of 10m/s, then what is it speed if the mass of the car increased by 20kg(so that the mass of the car now is 70kg)

Homework Equations

The Attempt at a Solution

what kind of equation should i use?
i was wondering if i can use the equation of kinetic energy?

 

[Infinitum]

Hi fondrika! Welcome to PF

The question is a bit strange. It does not specify how the mass of the car increased, because it could be due to any reason like an inelastic collision, or that the mass was just placed on the car, was there an acceleration(impulsive force) as the mass was increased? etc.

But just considering a mass added to the car without any external force acting on the car in the direction of its motion, I would probably use conservation of momentum.