How do I calculate the mass of a moving object?

[Joseph Hotto]

Homework Statement

Someone mistakenly threw away a lovely couch, and you decide to take it back to your apartment. You push it with a force of 350 Newtons and at 30 degrees below the horizontal at 2 m/s. The coefficents of friction are μs = 0.4 and μf = 0.3. What is the couch's mass?

Homework Equations

Fs = μsN
N = mgcosθ
F = ma

The Attempt at a Solution

Fs = (0.4) (350 N)
= 140 N <- Force of static friction
ΣFx = (350) = (2m/s) * M + 2 (0.4) * M - 2(0.3 M)
350N = mg (cos(330 degrees)
350 = 0.866 mg

 

[kuruman]

Reconsider your calculation of the force of friction.
The quantity (2 m/s)*M is not a force. The entire equaiton for ΣF_x is incorrect.