64. We take rightwards as the +x direction. Thus,
F
1
= 20ˆi in Newtons. In each case, we use Newton’s
second law
F
1
+
F
2
= ma where m = 2.0 kg.
(a)If a = +10ˆi in SI units, then the equation above gives
F
2
= 0.
(b)If a = +20ˆi m/s
2
, then that equation gives
F
2
= 20ˆi N.
(c)If a = 0, then the equation gives
F
2
=
−20ˆi N.
(d)If a =
−10ˆi m/s
2
, the equation gives
F
2
=
−40ˆi N.
(e)If a =
−20ˆi m/s
2
, the equation gives
F
2
=
−60ˆi N.