∑F = ma = (90 kg)(1.2 m/s²) = 108 N = 100 N (1 significant digit)
I think its B B)Warm water rises and cold water moves in to replace it.
Hi there!
We know that:
Force due to gravity = Mgsinθ
Force due to friction = μMgcosθ
Let the positive direction be directed in the direction of the block's acceleration, which is downward.
Thus:
ΣF = Mgsinθ - μMgcosθ
Solving for acceleration requires diving all terms by the mass, so:
a = gsinθ - μgcosθ
Substitute in given values. (g = 9.8 m/s²)
a = 9.8sin(30) - 0.3(9.8)cos(30) = 2.354 m/s²
When light travels from a medium with higher refractive index to a medium with lower refractive index, the critical angle is the angle of incidence above which light is reflected only (no refraction occurs), and the value of this critical angle is given by

where n2 is the refractive index of the second medium and n1 is the refractive index of the first medium.
In this problem, the first medium is the glass (

), while the second medium is oil (

), therefore the critical angle is given by