Question

A 48 kg pole vaulter running at 10 m/s vaults over the bar. Her speed when she is above the bar is 1.3 m/s. Neglect air resistance, as well as any energy absorbed by the pole, and determine her altitude as she crosses the bar.

Answer 1

Given : v_i = 10 m/s , v_f = 1.3 m/s , m = 48 kg

Constant : g = 9.81 m/s²

Solution:

Let the altitude as she crosses the bar is h_f and initial altitude be h_i

As , we've neglected any energy absorbed by the pole then energy is conserved .

Initial energy = Final energy

KE_i + PE_i = KE_f + PE_f

initial potential energy (PE_i)= 0 , as h_i = 0

(1/2)mv_i² +0 = (1/2)mv_f² + mgh_f

gh_f = (1/2)(v_i² - v_f²)

h_f = (1/2)(v_i² - v_f²)/g

= (1/2)[(10m/s)² - (1.3 m/s)²]/(9.81m/s²)

= 5.01 m

Answer : 5.01 m