Anonymous
Anonymous asked in Science & MathematicsZoology · 9 months ago

# Physics Word Problem Please?

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.

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• 9 months ago

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.

• 9 months ago

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)

• Anonymous
9 months ago

a) 28 m/s

b) 28 m/s

c) 28 m/s

Gravity is a conservative field