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Re: HRW CH 10. Problem 57



At 09:29 AM 1/6/2004, you wrote:

I would be obliged to know the comments of the
list members concerning the answers given to the
Problem 57 given at the end of the chapter 10 of
Fundamentals of Physics by Halliday, Resnick and
Walker (Sixth Edition). [below]


Tyrannosaurus Rex may have known from experience not [to walk]
particularly fast because of the danger of tripping, in which case
their short forearms would have been no help in cushioning the fall.
Suppose a T.Rex of mass m trips while walking, toppling over, with
its center of mass falling freely a distance of 1.5 m. Then its center
of mass descends an additional 0.3 m owing to compression of its
body and the ground. (a) In multiples of the dinosaur's weight, what
is the approximate magnitude of the average vertical force on the
dinosaur during its collision with the ground (during the descent of
0.3 m)? Now assume that the dinosaur is running at a speed of
19 m/s (fast) when it trips, falls to the ground, and then slides to a
stop with a coefficient of kinetic friction of 0.6. Assume that the
average vertical force during the collision and sliding is that in (a).
What approximately , are (b) the magnitude of the average total
force on it from the ground (again in multiples of its weight) and
(c) the sliding distance?

Answers
(a) 5mg (b) 7 mg (c) 5 m.

regards,
Sarma.


Initial response:
1) The answers are not in multiples of T Rex weights.
2) If answer a) is intended to represent 5000 kg
it is poorly abbreviated as 5mg instead of about 50kN



Brian Whatcott Altus OK Eureka!