Anonymous
Anonymous asked in Science & MathematicsZoology · 8 months ago

A slingshot fires a pebble from the top of a building at a speed of 14.0 m/s. the building is 31.0 m tall. Ignoring air resistance, find the speed with which the pebble strikes the ground when the pebble is fired a) horizontally, b) vertically straight up, c) vertically straight down.

Relevance

Have you been taught the conservation of energy?

Change in potential energy is the same no matter how it gets there.

Given no change in total mechanical energy,

v = sqrt(14^2 + 2*9.81*31) m/s

If not then use kinematics formulas.

• ... which will of course yield the same results.

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• You have to memorize trajectory equations.

Vo Horizontal

Vyf² = 0²+2*g*d = 19.6*31 = 24.65 at impact

Vxf = 14m/s at impact so

Vf² = 24.65²+14² = 28.3m/s at impact a)

Vo straight up

Find time of flight

31 +14*t - 4.9*t² = 0

t = 4.32

Vy(4.32) = 14 - 9.8*4.32 = -28.3m/s (down) at impact b)

Vo straight down

Vyf² = 14²+19.6*31 = 28.3²

28.3m/s (down) at impact c)

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• Anonymous
8 months ago

a) 28 m/s

b) 28 m/s

c) 28 m/s

Gravity is a conservative field

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