Question

A slingshot fi res 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, fi nd the speed with which the pebble strikes the ground when the pebble is fi red (a) horizontally, (b) vertically straight up, and (c) vertically straight down.

Answer 1

Answer:

Explanation:

given,

speed of the pebble = 14 m/s

height of the building = 31 m

ignoring air resistance

a) horizontally

 V_x = 14 m/s

time = $\sqrt{\dfrac{2h}{g}}$

time = $\sqrt{\dfrac{2\times 31}{9.8}}$

times  = 2.52 s

v_y = 9.8 x 2.52

v_y = 24.7 m/s

resultant velocity

      = $\sqrt{24.7^2+14^2}$

      = 28.39 m/s

b) vertically straight up

max height = $\dfrac{v^2}{2g}$

                   = $\dfrac{15^2}{2\times 9.8}$

                   = 11.47 m

height covered = 31 + 11.47

                          = 42.47 m

velocity = $\sqrt{2gh}$

             = $\sqrt{2\times 9.8 \times 42.47}$

             = 28.85 m/s

c) vertically down

v² = u² + 2as

v² = 2 × 9.8 × 31 +14²

v² = 803.6

v = 28.35 m/s