The electromagnet shown below is made up of a coil of electrical wire wrapped around an iron core.

which of the following would decrease the strength of this electromagnet?

a adding batteries to the circuit
b removing its iron core
c increasing the current through the coil
d increasing the number of wire loops in the coil

B. Removing its iron core

Explanation:

In an electromagnet role of its core is very important as it concentrate magnetic flux to make magnetic field more powerful. Generally core of electromagnet is made up of a ferromagnetic material or of a ferrimagnetic material such as iron. Adding batteries to the circuit and increasing the current through the coil and increasing loops in the coil will increase magnetic  strength of an electromagnet.

answer and explanation;

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.