Question

Name December 9th, 2018 Student # final test Prof. Ivan J. Baiges INGE 3032 Applied Mechanics - Dynamics PROBLEM 2 A 500 lbf reindeer (venado) goes down a 20° slope (with NO FRICTION ON THE SLOPE) from a height of 20 feet. At the bottom of the slope, the reindeer impacts a Christmas elf that has a weight of 120 lbf and is walking to the left at a speed of 3.5 ft/s when the impact occurs - determine the following i. If the coefficient of restitution e 0.65, what is the post impact velocity of the reindeer and the elf? What is the impulse between them? iii. ii. If the time the contact between the reindeer and the elf is te 0.2 sec, what is the average impact force between them? If the elf slides 20 feet after impact, what is the friction force that the elf feels after the impact? iv. reindeer Christmas elf height

Answer 1

This is a collision problem

a)

velocity of elf

Velocity of venado at the bottom

$v = \sqrt(2gh)$

u = v/(2 * 32.2 * 20) 35.9ft/s

This can be resolved into:

- 35.9cos20i - 35.9sin20j

33.73i _ 12.28 u

33.73 t1ro

Velocity after an inelastic collision is given by:

ejm2 VI + mi + m2 mi + m2

m2em1 1m1+m2 01 mi + m2

substituting e = 0.65 and masses and velocities, we get:

U2= 21.84ft/s

1,1-46.04ft/s

b)

Impulse is distruction of momentum

1 (500 * (33.73-21.84) + 120 * (-3.5-46.04))/32.2 0.0062

c)

average impact force:

F = 1/(0.2sec)

F0.0310

d)

If it slides 20ft after collision,

Its energy is absorbed by friction in that distance.