Arock is suspended by a light string. when the rock is in air, the tension in the string is 38.7 n . when the rock is totally immersed in water, the tension is 32.0 n . when the rock is totally immersed in an unknown liquid, the tension is 19.0 n .
what is the density of the unknown liquid?

Explanation:

When pendulum is in air then the tension in the string is given as

now when it is submerged in water then tension is decreased due to buoyancy force of water

so we will have

When rock is immersed in unknown liquid then tension is given by

from buoyancy force of water we can say

now for other liquid we will have

car stops. he keeps going = he has inertia

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.