What is the upward force on the hot air balloon?

[emma3001]

I have 2 problems that i can't do

You apply a force of 0.35N up to lift a fork. The resulting acceleration is 0.15m/s2 up. Determine the mass of the fork (the answer is 35g-why?)

A hot air balloon has acceleration of 1.10m/s2 down. The mass is 315kg.
What is the upward force on the system?
The balloonist wished to change acceleration to zero. Determine the mass of the ballast that must be discarded overboard (air resistance is neglected)

please help!

 

[emma3001]

i thought that Fnet=Fa-Fg=ma so i said that Fa=0.35N and a=0.15m/s2.

Then Fg=mg so 0.35N=m(9.8)
m=0.036kg but the answer is 35g so do u have to subtract 9.8ms2 from the given a?
I drew a FBD but i still am confused as to how to do it.

 

[Doc Al]

fork problem

i thought that Fnet=Fa-Fg=ma so i said that Fa=0.35N and a=0.15m/s2.

This is correct.

Then Fg=mg

Also true. Here's how you combine them:
Fa - Fg = ma
Fa - mg = ma
Fa = mg + ma
Fa = m(g + a)

Continue and solve for m.

 

[emma3001]

thank you very much-these concepts are hard to wrap my head around!