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.
Photons are particles of electromagnetic radiation.
Answer:
Magnetic force is equal to 
Explanation:
We have given electron is accelerated with a potential difference of 81700 volt.
Magnetic field B = 0.508 T
Angle between magnetic field and velocity 
Mass of electron 
Charge on electron 
By energy conservation.



Magnetic force on electron



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Answer:
The correct answer is D. Static friction is much stronger than kinetic friction, so it takes more force to get an object moving than it does to keep it moving.
Explanation:
We can eliminate choice A if we know that both static friction and kinetic friction depend on what are called the coefficients of static friction and kinetic friction, respectively. These coefficients are a reflection of the nature of the surface. In other words, both static friction and kinetic friction depend on the surface material (choice A is incorrect).
Choice B is incorrect because static friction applies to still (static) object whereas kinetic friction applies to moving objects (that have kinetic energy).
Choice C is also incorrect.
Choice D is correct as described in the given information. It takes much more force to start an object from rest than to keep it moving. Think about things in your everyday life - it takes a push to get a toy car moving along the ground, but you do not need to consistently push the car with the same force to keep it moving. This reflects that static friction is much stronger than kinetic friction, which is also described by the relationship between their coefficients (the coefficient of static friction is generally greater than that of kinetic friction).
Hope this helps!