6. A physics book slides off a horizontal table top with a speed of 1.25m/s. It strikes a floor in 0.4s.

What's the speed with which the book strikes the floor?

4.11 m/s

Explanation:

Given:

v₀ₓ = 1.25 m/s

aₓ = 0 m/s²

v₀ᵧ = 0 m/s

aᵧ = - 9.8 m/s²

t = 0.4 s

Find: v

First, in the x direction:

vₓ = aₓt + v₀ₓ

vₓ = (0 m/s²) (0.4 s) + 1.25 m/s

vₓ = 1.25 m/s

And in the y direction:

vᵧ = aᵧt + v₀ᵧ

vᵧ = (-9.8 m/s²) (0.4 s) + 0 m/s

vᵧ = - 3.92 m/s

The net speed is found with Pythagorean theorem:

v² = vₓ² + vᵧ²

v² = (1.25 m/s) ² + (-3.92 m/s) ²

v = 4.11 m/s