Answer:
The equivalent stiffness of the string is 8.93 N/m.
Explanation:
Given that,
Spring stiffness is
According to figure,
and 
is in series
We need to calculate the equivalent
Using formula for series
Put the value into the formula
k and 
is in parallel
We need to calculate the k'
Using formula for parallel
Put the value into the formula
,k' and 
is in series
We need to calculate the equivalent stiffness of the spring
Using formula for series
Put the value into the formula
Hence, The equivalent stiffness of the string is 8.93 N/m.
It is called the reaction force of a bird flying.
Answer: B. meteorites, UV rays
The earth's atmosphere plays an important role in shielding the space rocks and meteorites enters inside the earth due to collision with the celestial body. Due to high heat and pressure in the mesospheric layer of the atmosphere these meteorites burned up before reaching the biosphere or hydrosphere system of the earth. The UV rays are protected from entering into the earth atmosphere by the ozone layer present in the stratosphere of the atmosphere. Both meteorites and UV rays can negatively effect the human population. Therefore, the atmosphere is an agent which provides protection against them.
The car bounces off and moves in the opposite direction
