#### Externet

##### Well-Known Member

A speargun takes 80 lbs_force to arm its elastic sling (is that 36 Kg_force or 356 Newtons ?)

When triggered, its 1 Kg_

**weight**_in_water / 1 metre long spearshaft with 10mm diameter pointy arrowhead shoots with what

-Initial velocity,

-Kinetic energy

The media is water, density 1 g/ml.

[ The shape constant for the spearhead is ? (cannot find a table)

The initial impulse at full force gradually decreases to zero impulse in 0.1 seconds at firing when the spearshaft exits the gun and slings have collapsed ]

Formulas I believe are pertinent:

Vinitial = square root of 2 x kinetic energy / mass

Deceleration due to water resistance = density of media x area x shape constant x Vinitial^2 / 2 mass

Can the calculation steps and rationale be explained, please ?