When discharging a fire extinguisher, it is important to aim: a. On top of the flames b. At the top of the flames c. Anywhere d. At the base of the fire

d. At the base of the fire

Explanation:

Most fire extinguisher utilize the non-combustible nature of carbon-dioxide . carbon-dioxide is what is used in fire extinguishers, because it does not support burning. Also, carbon-dioxide is denser than air, allowing it to sink down. Aiming at the bottom of the flame allows the carbon-dioxide to sink down on the base of the flame, covering the base of the fire, and cutting off its supply of oxygen which is vital for combustion.

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.

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.