Always use significant figure rules. remember that these rules apply to all numbers that are measurements. calculate the force at sea level that a boy of mass 40 kg exerts on a chair in which he is sitting. n a. 390 b. 40. c. 4

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...?

force is based upon mass and acceleration.the statement is not always true.

it can be explained from newton's second law of motion.

as per newton's second law of motion the rate of change of momentum is directly proportional to the applied force and takes place along the direction of force.

mathematically it can be written as -

                                              ⇒      

here   k is the proportionality constant whose value is 1.

                                                            [a is the acceleration=dv/dt]

hence we see that force not only depends on mass and acceleration but also on velocity and rate of change of mass. force f will depend on mass and acceleration only when mass is constant.

hence the statement that force is based upon mass and acceleration is false.