Answer:
The density is 
Explanation:
From the question we are told that
The weight in air is 
The weight in water is 
The weight in a unknown liquid is 
Now according to Archimedes principle the weight of the object in water is mathematically represented as

Where
is he mass of the water displaced
substituting value


Now according to Archimedes principle the weight of the object in unknown is mathematically represented as

Where
is he mass of the unknown liquid displaced
substituting value


dividing equation 2 by equation 1


=> 
Now since the volume of water and liquid displaced are the same then

This because

So if volume is constant
mass = constant * density
Where
is the density of the liquid
and
is the density of water which is a constant with a value 
So


A- plane mirror because its surface is plane
Answer:
a.
b. 
Explanation:
<u>Given:</u>
- Velocity of the particle, v(t) = 3 cos(mt) = 3 cos (0.5t) .
<h2>
(a):</h2>
The acceleration of the particle at a time is defined as the rate of change of velocity of the particle at that time.

At time t = 3 seconds,

<u>Note</u>:<em> The arguments of the sine is calculated in unit of radian and not in degree.</em>
<h2>
(b):</h2>
The velocity of the particle at some is defined as the rate of change of the position of the particle.

For the time interval of 2 seconds,

The term of the left is the displacement of the particle in time interval of 2 seconds, therefore,

It is the displacement of the particle in 2 seconds.
Halogens<span> are extremely reactive elements because they need one more electron to gain a full octet of valence electrons, whereas the </span>noble gases<span>are extremely unstable because they already have their full octet.</span>