Hello!
What you are describing here is Newton's second law, this is very important to know because it gives you the equation to answer this question.
Newton's second law states:
Fnet = (mass) * (acceleration)
and its unit of measurement is the Newton (kg * m/s^2), that is dimensional analysis coming from -
mass = kg
acceleration = m/s^2
Since the equation is the mass times the acceleration, you do the same with the units so it gives you (kg * m/s^2) which is known as Newtons. (Just as a side note!)
On wards!
Known:
m = 2 kg
a = 20 m/s^2
Unknown:
Fnet = ?
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Alright we have 2 known's and 1 unknown, that's good because now we can solve for the net force!
Fnet = m * a
Fnet = 2 kg * 20 m/s^2
Fnet = 40 N
In conclusion, it takes 40 Newtons of force to accelerate a 2 kg rock 20 m/s^2 in gravity free space!
Hope this helps & good luck with your studies
P.S. Make sure you re-visit newtons second law so you can flex on everyone in class and be relaxed! It is a very important topic so I recommend khan academy videos, they are awesome!