Here when an object is placed on the level floor then in that case there are two forces on the object
1). Weight of object downwards (mg)
2). Normal force due to floor which will counterbalance the weight (N)
so when no force is applied on the box at that time normal force is counter balanced by weight.
Now here it is given that A person tried to lift the box upwards
So now there are two forces on the box
1). Applied force of person
2). Normal force due to ground
So now these two forces will counter balance the weight of the crate
So we can write an equation for force balance like

given that

here
m = 30 kg and
g = acceleration due to gravity = 10 m/s^2

now from above equation


So force applied by the person must be 150 N
100 MHz = 100,000,000 Hz = 10^8<span> Hz
And using basic conversions between frequencies, I've determined that the wavelength is roughly 3 meters.</span>
Answer:
We experience interference while listening to the radio. A radio station works by sending and receiving radio waves. Since the radio waves are being interfered with other waves which must have a wave nature.
The interference is the net result of two individual waves. It can be constructive or destructive interference and is the property of waves and not particles.
This interference is an example of electromagnetic radiation. Thus we experience wave behavior of electromagnetic radiation in our daily communications.
Answer:
Kinetic energy cannot be negative
potential energy is a reference dependent quantity and it can be positive as well as negative both
Since potential energy is defined only for conservative force so it can not be found for friction force
Explanation:
Kinetic energy of an object is given by the formula

here we know that
m = mass of object that can not be negative
v = speed of the object and since its square is given here so it can not be negative
so Kinetic energy is always positive
potential energy is given as the energy due to the virtue of the position of object
so it is

so potential energy is a reference dependent quantity and it can be positive as well as negative both
Since potential energy is defined only for conservative force so it can not be found for friction force
Answer:
Hubble measured the velocity of the movement of galaxies by using Hubble's law states that galaxies located farthest from the center of the universe than those closest to the center.
Explanation:
Hubble's Law says that an object's velocity away from an observer is directly proportional to its distance from the observer. In other words, the farther away something is the faster it is moving away from us. The spectrum of a galaxy allows you to measure its redshift.