Answer:
A lens placed in a transparent liquid becomes invisible because when refractive index of the material of the lens is equal to the refractive index of the liquid in which lens is placed under this condition no bending of light takes place when it travels from liquid to the lens, so both will start behaving like both are same things.
Explanation:
hope it helps :))
Answer: 
Explanation:
This problem can be solved by the following equation:

Where:
is the pressure difference between the two ends of the pipe
is the viscosity of oil
is the length of the pipe
is the Rate of flow of the fluid
is the diameter of the pipe
is the radius of the pipe
Soving for
:

Finally:

Answer:
Explanation:
The mass of the block is 0.5kg
m = 0.5kg.
The spring constant is 50N/m
k =50N/m.
When the spring is stretch to 0.3m
e=0.3m
The spring oscillates from -0.3 to 0.3m
Therefore, amplitude is A=0.3m
Magnitude of acceleration and the direction of the force
The angular frequency (ω) is given as
ω = √(k/m)
ω = √(50/0.5)
ω = √100
ω = 10rad/s
The acceleration of a SHM is given as
a = -ω²A
a = -10²×0.3
a = -30m/s²
Since we need the magnitude of the acceleration,
Then, a = 30m/s²
To know the direction of net force let apply newtons second law
ΣFnet = ma
Fnet = 0.5 × -30
Fnet = -15N
Fnet = -15•i N
The net force is directed to the negative direction of the x -axis