Hi there,

According to Newton's Second Law, the acceleration is determined by the *net* force. So, if we are lifting the 10 kg disc with a force of 145 N, we still have to account for the object's weight, which points downward. An object's weight is the gravitational force on the object, equal to mass times 10 m/s^2. So, the weight of the disc is 100 N.

Net Force = Force Up - Force Down = Force Applied - Weight = 145 N - 100 N = 45 N

Once we have *net* force, then we can solve for acceleration.

Hopefully that clarifies things a bit.

Cheers,

Jared Enns

Physics Instructor - MCAT Prep