Answer: below
Explanation: 1kg of steel is slightly heavier than 1 kg of feathers. 1 kg of feather will displace more air as the density of feather is very less comparitively. More the volume displaced more is the upthrust and less the apparent weight.
Greenhouse gasses in the upper atmosphere trap heat from the Earth and reflect it back down rather than allow it to escape. This makes Earth progressively warmer.
<h2>
Answer:</h2>
400N/m
<h2>
Explanation:</h2>
When n identical springs of stiffness k, are attached in series, the reciprocal of their equivalent stiffness (1 / m) is given by the sum of the reciprocal of their individual stiffnesses. i.e
= ∑ⁿ₁ [
] -----------------------(i)
That is;
=
+
+
+ . . . +
-------------------(ii)
If they have the same value of stiffness say s, then equation (ii) becomes;
= n x
-----------------(iii)
Where;
n = number of springs
From the question,
There are 3 identical springs, each with stiffness of 1200N/m and they are attached in series. This implies that;
n = 3
s = 1200N/m
Now, to calculate the effective stiffness,m, (i.e the stiffness of a longer spring formed from the series combination of these springs), we substitute these values into equation (iii) above as follows;
= 3 x 
= 
= 
Cross multiply;
m = 400N/m
Therefore, the stiffness of the longer spring is 400N/m