Projectiles question help maths

Hi, for projectile motion questions, I was wondering, if you get one value of v for in the vertical plane and one value of v in the horizontal plane, to find the final value of v, do you do Pythagoras i.e. the square root of the first v squared plus the second v squared? If so, why is this? Many thanks

Reply 1

Marcus_:D

20

To find the magnitude of the velocity or speed you need to do pythagoras since there is a vertical and horizontal component they particle is travelling in. Pythagoras does not consider direction.

Otherwise, if you require the velocity, you should be allowed to state the components separately in terms of i and j m/s or find the speed using pythagoras and use trigonometry to find the angle with respect to the horizontal.

Reply 2

Bertybassett

OP

11

Original post by Marcus_:D

To find the magnitude of the velocity or speed you need to do pythagoras since there is a vertical and horizontal component they particle is travelling in. Pythagoras does not consider direction.

Otherwise, if you require the velocity, you should be allowed to state the components separately in terms of i and j m/s or find the speed using pythagoras and use trigonometry to find the angle with respect to the horizontal.

thanks

Original post by Bertybassett

Hi, for projectile motion questions, I was wondering, if you get one value of v for in the vertical plane and one value of v in the horizontal plane, to find the final value of v, do you do Pythagoras i.e. the square root of the first v squared plus the second v squared? If so, why is this? Many thanks

If

\mathbf{v} = \begin{pmatrix} v_x \\ v_y \end{pmatrix}

then

|\mathbf{v}|

is the magnitude of this velocity vector... which is the speed.

In the diagram below, this is precisely the length of the purple line. Since the purple vector is made up from the red and grey one, which are perpendicular, you apply Pythagoras' Theorem to determine the length of this purple hypotenuse.

Projectiles question help maths

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