Ablock weighing 3.7 kg is suspended from the ceiling of a truck trailer by a hanging bungee cord. the cord has a cross-sectional area 40 mm2 and an unstretched length of 43 cm.
the truck begins stopped at a red light on a state highway. while stopped, the block hangs straight down to a distance 53 cm below the hook that attaches the bungee cord to the ceiling of the truck.

(a) what is the young's modulus of the cord?

Explanation:

Natural length of the string is given as

length of the string while block is hanging on it

extension in length is given as

now we have strain in the string is given as

similarly we will have cross-sectional area of the string is given as

now the stress in the string is given as

Now Young's Modulus is given as

i think its

the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

hope this !

im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.