This problem is taken from Ahlborn\'s Zoological Physics, P 5.2. Two young peopl

Question

This problem is taken from Ahlborn's Zoological Physics, P 5.2. Two young people jump down from a height of h = 2.0 m onto the forest floor which has a mud hole and a rocky flat. The boy (M = 70 kg) lands with stiff legs on the muddy ground, which "gives" so that he depresses the ground by Delta_y = 5 cm when being decelerated from the impact velocity U_0 to 0. Determine the impact speed U_0. Calculate the deceleration (negative acceleration of the center of mass of the boy during landing), and determine the force on the soles of his shoes during impact. The girl (M = 65 kg) lands on the rock, but in order to reduce the impact force she lands with soft knees and moves her center of gravity relative to her feet by Delta y = 0.5 m as she lands. What is the impact force on her soles of the feet during the landing?

Explanation / Answer

(a) Using conservation of energy

(Potential energy at height) + (kinetic energy at height) = (Potential energy at ground) + (kinetic energy at ground)

(mgh) + (1/2m*02) = (mg*0) + (1/2 mUo2)

Uo = (2gh)1/2

Uo = (2 * 9.8 * 2)1/2

Uo = 6.26 m/s

-----------------------------------------------------------------------------------

(b) Using relation v2 - Uo2 = 2ay

0 - (6.26)2 = 2 a (0.05)

a = - 391.88 m/s2

----------------------------------------------------------------

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.