No, we cannot touch gravity nor can we physically see it. We can only see how it works.
Answer:
A) 15.0 years
Explanation:
Due to the distance to the star system is in light-year units, we can compute the time by using:

then, Rob will take to complete the trip about 15 light-years.
hope this helps!!
Answer:
Work done against gravity will be
W = Mgℓ
Explanation:
Work done to raise the mass from ground to given height is against gravity
So here work done is given by the formula

here we know that

it is the force due to gravity which is also known as weight
so here distance moved by the object is given as
d = ℓ
now work done is given as
W = Mg ℓ