Explanation:
C is correct.
Newton second law states that force is directly proportional to acceleration with m being the constant of variation.

So


A is wrong, the constant g only happens in free fall or in vertical direction
B and D are wrong due to the mathematical error or equation error
Answer: 4 ft/s
Explanation:
Given
height of man
speed of person 
height if street light
Let x be the distance between person and street light and y be the length of his shadow
From diagram
as the two triangle ADE and ABC are similar therefore we can say that




differentiate above Equation w.r.t time we get


Answer:

Explanation:
As per mechanical energy conservation we can say that here since friction is present in the barrel so we will have
Work done by friction force = Loss in mechanical energy
so we will have

here we know that



Initial compression in the spring is given as



now from above equation



