# MotionWatch

#1
I don't get why the initial velocity is 0 when you fire a rifle. This is from one of the past paper questions. I know the initial velocity = 0 when you drop something, and when you throw something up initial velocity ≠ 0. But I don't understand the case when you fire something horizontally.
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7 months ago
#2
The initial velocity is not zero - the initial VERTICAL velocity is zero if you fire horizontally.

Put it another way, a horizontal velocity has zero vertical component.
Last edited by phys981; 7 months ago
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#3
(Original post by phys981)
The initial velocity is not zero - the initial VERTICAL velocity is zero if you fire horizontally.

Put it another way, a horizontal velocity has zero vertical component.
Right, I sort of get it now. But how about final vertical velocity?
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7 months ago
#4
You have to calculate that using equations of motion.

You do it exactly as though the object had been dropped - in other words the fact that it is moving horizontally has NO effect on the vertical velocity.
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