2. We apply Newton’s second law G (Eq.G 5-1G or, equivalently, Eq. 5-2). The net force applied on the chopping block is Fnet = F1 + F2 , where the vector addition is done using G G G unit-vector notation. The acceleration of the block is given by a = F1 + F2 / m.
d
i
(a) In the first case G G F1 + F2 = ª¬( 3.0N ) ˆi + ( 4.0N ) ˆj º¼ + ª¬( −3.0N ) ˆi + ( −4.0N ) ˆjº¼ = 0
G so a = 0 . G (b) In the second case, the acceleration a equals G G F1 + F2 = m
(( 3.0N ) ˆi + ( 4.0N ) ˆj) + (( −3.0N ) ˆi + ( 4.0N ) ˆj) = (4.0m/s )ˆj. 2
2.0kg
G (c) In this final situation, a is G G F1 + F2 = m
(( 3.0N ) ˆi + ( 4.0N ) ˆj) + (( 3.0N ) ˆi + ( −4.0N ) ˆj) = (3.0 m/s )i.ˆ 2
2.0 kg
