F = m • a
What we know:
- Gravity: 9.8 m/s
- Force: 490 N
Equation derived:
m = F/a
m = 490/9.8
= 50 kg
Answer:
Required charge 
.
Explanation:
Given:
Diameter of the isolated plastic sphere = 25.0 cm
Magnitude of the Electric field = 1500 N/C
now
Electric field (E) is given as:
where,
k = coulomb's constant = 9 × 10⁹ N
q = required charge
r = distance of the point from the charge where electric field is being measured
The value of r at the just outside of the sphere = 
thus, according to the given data
or
or
Required charge .
Now,
the number of electrons (n) required will be
or
or
The last choice on the list is the correct one, for both #2 and #3.
Answer:
2.The density of air increases and thendecreases as the sound wave passes.
Explanation:
Sound waves are mechanical waves, which consist of oscillation of the particles in the medium where the wave is transmitted through.
Sound waves are also longitudinal waves, which means that the direction of oscillations of the particles of the medium occurs in a direction parallel to the direction of motion of the wave (so, essentially back and forth).
Due to the nature of longitudinal waves, they create alternating regions of the medium where the density of particles are higher and lower. The former are called compressions, while the latter are called rarefactions.
Therefore, when a sound wave travels through the air, the density of one region of air continuously changes: compression first (high density), rarefaction then (lower density), then compression again, etc..
