(a) The net force upward force of the helicopter is -35,880 N.
(b) The weight of the helicopter is 45,080 N.
(c) The lift-force exerted by the air on the propellers is 9,200 N.
The given parameters:
The net force upward force of the helicopter is calculated as follows;
[tex]F = ma - mg\\\\F = m(a - g)\\\\F = 4600(2 - 9.8)\\\\F = - 35,880 \ N[/tex]
The weight of the helicopter is calculated as follows;
[tex]W = mg\\\\W = 4600 \times 9.8\\\\W = 45,080 \ N[/tex]
The lift-force exerted by the air on the propellers is calculated as follows;
[tex]F = ma\\\\F = 4600 \times 2\\\\F = 9,200 \ N[/tex]
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