When you throw a pebble straight up with initial speed V, it reaches a maximum height H with no air resistance. At what speed should you throw it up vertically so it will go twice as high?

Respuesta :

Answer:

Explanation:

Given

Initial speed is u=V

Maximum height of Pebble is H

Deriving maximum height of Pebble and considering motion in vertical direction

[tex]v^2-u^2=2 as[/tex]

where v=final velocity

u=initial velocity

a=acceleration

s=Displacement

Final velocity will be zero at maximum height

[tex]0-(V)^2=2\times (-g)\cdot H[/tex]

[tex]H=\frac{V^2}{2g}[/tex]

i.e. maximum height is dependent on square of initial velocity

for twice the height

[tex]2H=\frac{(V')^2}{2g}[/tex]

on comparing

[tex]V'=\sqrt{2}V[/tex]

The speed needed for the pebble to go twice as high is a factor of √2

Newton's law of motion is given by:

v² = u² + 2gH

Where v is the final velocity, u is the initial velocity, g is the acceleration due to gravity and H is the height.

At maximum height, v = 0, g is negative(going up), hence:

0 = u² - 2gH

H = u²/2g

u = √(2gH)

To go twice as high:

u' = √(2g*2H) = u√2

The speed needed for the pebble to go twice as high is a factor of √2

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