The person is standing on the floor of the elevator, and he isn't
floating up or smashing through the floor.
So the person's acceleration is exactly the same as the elevator's
acceleration.
Now, Newton's second law of motion says:
F = M · a
(the net force on the person) = (the person's mass) x (his acceleration)
Net force = (80 kg) x (0.5 m/s²)
= 40 newtons .
The correct answer is
D.
unbalanced forces
In fact, according to Newton's second law, unbalanced forces acting on an object will accelerate the object:
where the term on the left is the resultant of the forces acting on the object, m is the object's mass, and a is its acceleration.
If there are unbalanced forces acting on the object, the acceleration of the object a is different from zero: this means that the object will change its speed or its direction, or it can also stop moving if the direction of the force is opposite to that of the motion.
The density of a material is given by:
where
d is the density
m is the mass of the sample
V is its volume
In our problem, the material has a mass of m=2.75 g and a volume of
, so its density is:
So, the correct answer is D).
The turn and voltage ratio of a transformer can be simply expressed by the equation:
Ns/Np = Vs/Vp; where N is the number of turns and V is the voltage.
Plugging in the given values, we have:
25 turns / 100 turns = Vs / 40 volts
Vs = 40 volts (25 turns/100 turns)
Vs = 10 volts
The answer is D.