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A 28.5-Newton force is applied at a 30-degree angle to the horizontal to accelerate a 6.5-kg box across a rough surface (coefficient of friction = 0.22). Use g = 9.8 m/s/s to find frictional force (F(frict)) , normal force (F(norm)) , gravitational force (F(grav)) , and acceleration (a). Enter each answer accurate to the first decimal place.

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Answer:

Frictional force (F(frict)) = 17.1 N

Normal force (F(norm)) = 78.0 N

Gravitational force (F(grav)) = 63.7 N

Acceleration (a) = 1.2 ms⁻²

Step-by-step explanation:

Newton's second law:

[tex]\boxed{F_{net}=ma}[/tex]

where:

  • [tex]F_{net}[/tex] = overall resultant force.
  • m = mass.
  • a = acceleration.

Use trigonometry to resolve the 28.5 N force into its horizontal and vertical components since it is acting on the particle at 30°:

[tex]\implies F_x=28.5 \cos 30^{\circ}[/tex]

[tex]\implies F_y=28.5 \sin 30^{\circ}[/tex]

Weight (mg)

Due to the particle's mass, m, and the acceleration due to gravity, g:

[tex]\boxed{W=mg}[/tex]

Given:

  • m = 6.5 kg
  • g = 9.8 ms⁻²

[tex]\begin{aligned}W & = mg\\\implies W & = 6.5 \times 9.8\\W & = 63.7\;\sf N\end{aligned}[/tex]

Normal reaction (R)

The particle is moving parallel to the plane (the horizontal), so acceleration perpendicular to the plane is zero.

Resolving forces vertically (taking ↑ as positive):

[tex]\begin{aligned}F & = ma\\\implies R-W-28.5 \sin 30^{\circ}&=6.5 \times 0\\R-W-28.5 \sin 30^{\circ}&=0\\R & = W+28.5 \sin 30^{\circ}\\R & = 6.5(9.8)+28.5(0.5)\\R & = 63.7+14.25\\R & = 77.95\\R & = 78.0 \;\; \sf N\; (1\:d.p.)\end{aligned}[/tex]

Frictional force (F)

When a moving object is acted on by a frictional force, fiction is limiting, and the frictional force F is at its maximum value:

[tex]\boxed{F = \mu R}[/tex]

(Where μ is the coefficient of friction and R is the normal reaction).

[tex]\begin{aligned}F & = \mu R\\\implies F & = 0.22 \times 77.95\\F & = 17.149\\F & = 17.1 \;\; \sf N\;(2\:d.p.)\end{aligned}[/tex]

Acceleration (a)

Friction always acts in the opposite direction to motion (or potential motion).

Resolving forces horizontally (taking → as positive):

[tex]\begin{aligned}F & = ma\\\implies 28.5 \cos 30^{\circ}-F & = 6.5a\\28.5 \left(\dfrac{\sqrt{3}}{2}\right)-17.149 & = 6.5a\\\dfrac{57\sqrt{3}}{4}-17.149 & = 6.5a\\7.532724008 & = 6.5a\\a & = 1.158880617\\a & = 1.2\; \sf ms^{-2}\;\;(1\:d.p.)\end{aligned}[/tex]

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