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Re: HRW CH 10. Problem 57



On 6 Jan 2004, at 8:31, David T. Marx wrote:

Can you send us the problem and answers given?

Here is it - a long one.

Tyrannosaurus Rex may have known from experience not
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.