Answers to homework problems:

Chapter 4.
 3) No. Object has same mass on Earth and on the Moon therefore it has
    same inertia.
18) F = m*a  --> m = F/a = 200 N/0.75 (m/s^2)=266.67 kg
    weight = m*g = 266.67 kg*9.8 (m/s^2)=2613.3 N
19) F = m*a = 70000000 kg*0.1 m/s^2=7*10^6 N
30) F = m*a . 
    The acceleration a = change of velocity/time = (90-0)km/h / 4.5 s =
    90,000m/3600s/4.5s = 5.56 m/s^2.
    F = 60 kg * 5.56 m/s^2 = 333.33 N
43) assume a pointing down on the left side (if assumption is wrong I'll get
    a negative sign in the solution). There are two string tension forces -
    T1 acting between m1 and m3 and T2 acting between m3 and m2.
    Newton's law for m1:  m1*g - T1 = m1*a
    Newton's law for m2:  m2*g - T2 = - m2*a
    Newton's law for m3:  T1 - T2 = m3*a
    solution  --> a = (m1 - m2)/(m1+m2+m3) * g
    a)  a = -0.25 g = -2.45 m/s^2
    b)  a = 0,2 g = 1.96 m/s^2
48) a) 70 kg * 9.8 m/s^2 = 686 N
    b) 70 kg * (9.8 + 0.525) m/s^2 = 723 N
    c) 70 kg * (9.8 - 0.525) m/s^2 = 649 N
53) Forces acting on different objects cannot cancel
59) Lets consider the bullet first:
    The velocity equation: v^2 = v0^2 + 2 * a * x
    ---> acceleration a = (v^2 - v_0^2)/(2*x)
    since initial velocity v0 = 0 then a = v^2/(2*x)= (300m/s)^2/(2*0.75m)
    a = 60 000 m/s^2
    The force on a bullet is F = m*a = 0.025 kg * 60 000 m/s^2 = 1500 N
    The force on the rifle has the same magnitude.