# 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.

### 3 Answers

- RealProLv 73 weeks agoFavorite Answer
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.

- oldschoolLv 73 weeks 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)

- Anonymous3 weeks ago
a) 28 m/s

b) 28 m/s

c) 28 m/s

Gravity is a conservative field

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