Whoa, whoa... settle down there. We'll sort you out.
All of your questions in life can be solved using one simple formula: F = m*a
In english, this is Force = (mass)*(acceleration) --------------------------------- [1] Let's identify the mass. Kg (kilograms) is a mass unit, so we know that m = 40. The acceleration is a = 10 m/s^2.
The question is, is the force 400 N? Let's check against the formula: F = m*a F = (40 kg)*(10 m/s^2) F = 400 kg*m/s^2 F = 400 N
Yes. The answer is true. --------------------- [2] The mass is m = 60 kg. The acceleration is a = 2.0 m/s^2. The force is F = m*a F = (60 kg)*(2.0 m/s^2) F = 120 kg*m/s^2 F = 120 N.
------------------ [3] The mass is m = 30 kg. The force is 180 N. Ah, this is a little different, now we don't know the acceleration. But the same formula works: F = m*a 180 N = (30 kg)*a 180 N / 30 kg = a 6.0 m/s^2 = a
The acceleration is 6.0 m/s^2. -------------------- [4] This is a hypothetical question. Suppose we know the force F and the acceleration a, but we don't know the mass m. I'll put m in a box [m] so that we remember that this is the one we don't know. The same formula works: F = m*a F = [m]*a <--- m is the one we don't know F / a = [m]
In reality, we would have numbers for F and a, but since we are just pretending we are done!
m = F/a is the formula. ---------------------- See? Not too bad. :)
