← Vectors: drawing, measuring and combining

Resultant direction by tangent

A driveway rises 6 m over a 10 m run. Enter its climb angle in degrees, to the nearest degree. Answers within 1° are accepted.

The perpendicular pair from the Pythagoras lesson: 6 m/s east and 8 m/s north made a 10 m/s resultant. That settles the magnitude. But a resultant is a vector, so it also needs a direction.

What angle does the resultant make with east?

The two perpendicular vectors and their resultant form a right triangle, with the resultant as the hypotenuse. Mark the angle at the resultant's tail, between the eastward vector and the resultant.

6 m/s east8 m/s northresultant: 10 m/sθ
The angle θ sits at the resultant's tail, between east and the resultant.

The northward 8 m/s sits across from that angle: it is the opposite side. The eastward 6 m/s touches the angle and is not the longest: it is the adjacent side. So tan θ = opp / adj = 8 / 6 ≈ 1.33. And θ = tan⁻¹(8 / 6) ≈ 53°.

State the direction against its reference: the resultant points 53° north of east. Report the resultant in full: 10 m/s, 53° north of east.

6 m/s east8 m/s northresultant: 10 m/s53°
tan θ = 8 / 6, so θ = tan⁻¹(8 / 6) ≈ 53°: the resultant in full is 10 m/s, 53° north of east.
Divide the magnitude of the vector the angle opens toward by the magnitude of the vector it is measured from: θ = tan⁻¹(opp / adj). Swapping them gives tan⁻¹(6/8) ≈ 37°, the same direction described from the other reference: 37° east of north.

A robot drives 24 m east, then 10 m north. Calculate the direction of its resultant displacement, as an angle north of east, to the nearest degree.

Write down the values in the question:

opp = 10 m (north), adj = 24 m (east), θ = ?

Write down the equation:

θ = tan⁻¹(opp / adj)

Substitute in the values:

θ = tan⁻¹(10 / 24) = tan⁻¹(0.417)

θ ≈ 23°: the resultant points 23° north of east.

Two perpendicular displacements: 20 m east and 11 m north. Enter the resultant's angle north of east, to the nearest degree. Answers within 1° are accepted.

Two perpendicular velocities act on a glider: 9 m/s east and 21 m/s north. Calculate the resultant's direction as an angle north of east, to the nearest degree.

Write down the values in the question:

opp = 21 m/s (north), adj = 9 m/s (east), θ = ?

Write down the equation:

θ = tan⁻¹(opp / adj)

Substitute in the values:

θ = tan⁻¹(21 / 9) = tan⁻¹(2.33)

θ ≈ 67°: the resultant points 67° north of east.

Two perpendicular velocities: 7 m/s east and 18 m/s north. Enter the resultant's angle north of east, to the nearest degree. Answers within 1° are accepted.

A resultant combines 12 m east and 31 m north. Which calculation gives its angle north of east?

Your turn

Two perpendicular velocities act on a boat: 16 m/s east and 30 m/s north. Enter the resultant's angle north of east, to the nearest degree. Answers within 1° are accepted.

A rover drives 45 m east, then 24 m north. Enter the direction of its resultant displacement as an angle north of east, to the nearest degree. Answers within 1° are accepted.

Two perpendicular velocities: 14 m/s west and 25 m/s north. Enter the resultant's angle north of west, to the nearest degree. Answers within 1° are accepted.