Physics help please! Concerning Newton's Second Law...?

Yaya

New member
When empty, a particular helicopter of mass 3770 kg can accelerate straight upward at a maximum acceleration of 1.43 m/s2. A careless crewman overloads the helicopter so that it is just unable to lift off. What is the mass of the cargo?



I have attempted to solve the problem in the following manner...

helicopter mass = m (3770 kg= 36971 N)

Apply Newton's 2nd Law net F=ma
F - mg = ma, solve for F
so... F= ma/(-mg)
Apply the equation again now with cargo M and a=0 (just unable to lift
off). Same F:

F - (m + M)g = (m + M)a, solve for M, the only unknown.

I ended up with 65.6 Kg... what am I doing wrong?
 
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