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wata asked in Science & MathematicsPhysics · 1 decade ago

Basic physics question - Vector nature of forces: Forces in two dimensions?

An object is being acted upon by three forces and moves with a constant velocity. One force is 60.0 N along the x-axis, the second is 75.0 N along a direction making a counterclockwise angle of 150.0° with the x-axis. What is the magnitude and direction of the third force, measured counterclockwise from the x-axis?

Update:

Two different types of answers.

Angles

A) 182

B) 262

C) 226

D) 255

E) 128

Magnitude

A) 62.4 N

B) 135 N

C) 67.5 N

D) 38.8 N

E) 130 N

Please explain it. I need to study these type of questions for upcoming test.

Update 2:

To electron1

Actually your answer is what I got when I tried to solve it. But it's not on the multiple question choice so I thought I did something wrong. This is why I posted it on here.

2 Answers

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  • 1 decade ago
    Favourite answer

    An object is being acted upon by three forces and moves with a constant velocity. One force is 60.0 N along the x-axis, the second is 75.0 N along a direction making a counterclockwise angle of 150.0° with the x-axis. What is the magnitude and direction of the third force, measured counterclockwise from the x-axis?

    I assume that the angle of 150.0° with the x-axis means the 150.0° counterclockwise from the positive x-axis. This means the 2nd velocity vector has a negative x-component and a positive y-component

    Since the object moves with a constant velocity, the acceleration = 0

    So, the sum of the forces in the x and y directions = 0

    Sum of x-components = F * cos θ + 60 + (75 * cos 150) = 0

    F * cos θ + 60 + -64.95 = 0

    F * cos θ = 4.95 = x component of F

    Sum of y-components = (F * sin θ) + (75 * sin 150) = 0

    F * sin θ = -37.5 = y-component of F

    Since the x-component is positive and the y-component is negative, the force vector is in the quadrant with +x and –y.

    F * sin θ ÷ F * cos θ = tan θ

    tan θ = -37.5 ÷ 4.95

    θ = tan^-1 (-37.5 ÷ 4.95) = -82.48°

    This means the force vector is 82.48° clockwise from the positive x-axis, so the force vector is 360° – 82.48 = 277.52° counterclockwise from the positive x-axis.

    F * sin -82.48° = -37.5

    F = 37.82 N

    F * cos -82.48° = 4.95

    F = 37.82 N

    3rd Force = 37.82 N at angle of 277.52° counterclockwise from the positive x-axis.

  • ?
    Lv 4
    5 years ago

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