Amy is pulling a wagon with a force of 30 pounds up a hill at an angle of 25°. Give the force exerted on the wagon as a vector and as a linear combination of unit vectors i and j.

From statement we know that force exerted on the wagon has a magnitude of 30 pounds-force and an angle of 25° above the horizontal, which corresponds to the +x semiaxis, whereas the vertical is represented by the +y semiaxis.

The force ([tex]\vec F[/tex]), in pounds-force, can be modelled in two forms:

Vector (ordered pair - rectangular form)

[tex]\vec F = \left(\|\vec F\|\cdot \cos \theta, \|\vec F\|\cdot \sin \theta\right)[/tex] (1)

Vector (ordered pair - polar form)

[tex]\vec F = \left(\|\vec F\|, \theta\right)[/tex]

Sum of vectorial components (linear combination)

[tex]\vec {F} = \left(\|\vec F\|\cdot \cos \theta\right)\cdot \hat{i} + \left(\|\vec F\|\cdot \sin \theta \right)\cdot \hat{j}[/tex] (2)

Where:

[tex]\|\vec F\|[/tex] - Norm of the vector force, in newtons.

[tex]\theta[/tex] - Direction of the vector force with regard to the horizontal, in sexagesimal degrees.

[tex]\hat{i}[/tex], [tex]\hat{j}[/tex] - Orthogonal axes, no unit.

If we know that [tex]\|\vec F\| = 30\,lbf[/tex] and [tex]\theta = 25^{\circ}[/tex], then the force exerted on the wagon is:

Vector (ordered pair - rectangular form)

[tex]\vec F= \left(30\cdot \cos 25^{\circ}, 30\cdot \sin 25^{\circ}\right)\,[lbf][/tex]

[tex]\vec F = (27.189,12.679)\,[lbf][/tex]

Vector (ordered pair - polar form)

[tex]\vec F = (30\,lbf, 25^{\circ})[/tex]

Sum of vectorial components (linear combination)

[tex]\vec F = (30\cdot \cos 25^{\circ})\cdot \hat{i} + (30\cdot \sin 25^{\circ})\cdot \hat{j}\,[N][/tex]

[tex]\vec F = 27.189\cdot \hat{i} + 12.679\cdot \hat{j}\,[N][/tex]