Question

ALWAYS use significant figure rules. Remember that these rules apply to all numbers that are measurements.

Answer 1

Answer:

Well I'm going to go with A.

Explanation:

As per the question the mass of the boy is 40 kg.

The boy sits on a chair.

We are asked to calculate the force exerted by the boy on the chair at sea level.

The force exerted by boy on the chair while sitting on it is nothing else except the force of gravity of earth i.e the weight of the body .The direction of that force is vertically downward.

At sea level the acceleration due to gravity g = 9.8 m/s^2

Therefore, the weight of the boy  [m is the mass of the body]

we have m = 40 kg.

                             Therefore, w = 40 kg ×9.8 m/s^2

                                             =392 N kg m/s^2

                                              = 392 N

392 is not an option but I'm guessing you can round down 2 .to option A. 390...?