Two horizontal forces F1 and F2 are acting on a box but only F1 isshown pointing

Question

Two horizontal forces F1 and F2 are acting on a box but only F1 isshown pointing to the right along the x axis. F2 can eitherpoint to the right or the left. The box moves only along the xaxis. There is no friction between the box and the surface.
Suppose F1= 9N and the mass of the box is 3.0kg. Findthe magnitude and direction of the F2 when the acceleration of thebox is a) 5.0m/s2, b) -5.0m/s2, c) 0m/s2.
Suppose F1= 9N and the mass of the box is 3.0kg. Findthe magnitude and direction of the F2 when the acceleration of thebox is a) 5.0m/s2, b) -5.0m/s2, c) 0m/s2.

Explanation / Answer

(a)   acceleration, a = net force /mass          netforce = m a = 3 ( 5 ) = 15 N          Net force isalong the +ve x-axis           Sincenet force is +ve, the second force also must be along +vex-axis                    net force = F1 + F2                15 = 9 + F2                     F2 = 6 N ( right )    (b) net force = ma = 3 ( - 5) = - 15 N           netforce is along -ve x-axis           Sincenet force is along -ve x-axis, the second force must be along -vex-axis                      net force =F1 + F2                     -15 = F1 + F2                     F2 = - 24 N ( left )                15 = 9 + F2                     F2 = 6 N ( right )    (b) net force = ma = 3 ( - 5) = - 15 N           netforce is along -ve x-axis           Sincenet force is along -ve x-axis, the second force must be along -vex-axis                      net force =F1 + F2                     -15 = F1 + F2                     F2 = - 24 N ( left )                     F2 = - 24 N ( left )

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