Only two horizontal forces act on a 3.0 kg body that can move over a frictionless floor. One force is 9.0 N, acting due east, and the other is 8.0 N, acting 62° north of west. What is the magnitude of the body's acceleration?


Answer in the book (with no workings) says 2.9m/s2


I get ~1.7m/s2


F(net,x) = ma

F1(x) = 9.0N

F2(x) = -8.0cos(62) = ~ -3.8N


F(net,x) = F1(x) + F2(x) = 9.0N - 3.8N = 5.2N


5.2N = 3.0kg * a(m/s2)

a = 5.2N / 3.0kg = ~1.7m/s2


Seems like a straight forward question, what am I doing wrong?

Guest Mar 12, 2017

2+0 Answers


the forces acting laterally are

+9  N to the east

and  -8cos62 = -3.755 N

Net force is +5.244  east      f= ma     5.244 = 3 kg a       a = 1.75 m/s^2 east

Either the book has the wrong answer or the wrong info in the question!     

Good job !

ElectricPavlov  Mar 12, 2017

..as an 'aside'   if the angle is 6.2 degrees north of west, the answer comes out to a = 2.87 m/s^2

  Maybe there is a typo in the angle of the 8N force ??

ElectricPavlov  Mar 12, 2017

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