Answer:
the duration between any two events is called time. It's si unit is second.
Dark matter has been detected by its gravitational pull.
Explanation:
Density is measured in kg⋅m−2 . This means that it is derived from fundamental units which are the kilogram and metre.
Answer:
Part a)

Part b)

Part c)

Part d)

Explanation:
Part a)
As we know that speed of package is same as that of helicopter in horizontal direction
So after time "t" the velocity in x direction will remain constant while in Y direction it will go free fall
So we have



Part b)
Distance from helicopter is same as the distance of free fall
so we will have

Part c)
If helicopter is rising upwards with uniform speed
then final speed of the package after time t is given as


Part d)
distance from helicopter

The only kinds of radiation they can detect are visible light, which allows them to see, and infrared light, which they feel as warmth on their skin.