Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: HRW CH 10. Problem 57



You asked re Problem 57, chap 10, Fundamentals of Physics
Halliday, Resnick and Walker (Sixth Edition):

Is answer a) = 5 justified?

The T Rex was standing before it tripped.
It would be reasonable to take the surface at which its feet were
resting as the surface level. This surface was taking the animal's
weight initially. So depression of the surface would be due to
the excess deceleration force NOT the animals normal weight?

For v^2 = 2 a x
v = sqrt (3.g) = 5.42 m/s

Average force to decelerate a mass m dropping at 5.42 m/s in 0.3 meters?

v^2 = 2 a x again:
5.42 ^2 = 0.6 a
therefor a = 49 m/s^2 = 5g
and f = m a
so f av = 5 m g

( You will notice however I used an equation of constant acceleration to model
the ground deceleration)

I will pass over the other parts which treat the transient deceleration as
quasi static.

Brian W

At 05:48 PM 1/8/2004, you wrote:
Answers to (b) and (c) follow if we take normal reaction of ground to
be 6 times the weight. Compression of 0.3 m includes not only the
one due to the down ward motion of the body but also due to the
weight of the body. For (a) is the answer 5 times the weight of the
body justified?

regards,
Sarma.

On 7 Jan 2004, at 20:02, Brian Whatcott wrote:

> Now hold on a darn minute: I finally got a clue about the questions,
> and shared the same puzzlement at the prolix answers - after the
> first one anyway.
>
> Only one person seemed to really share my concerns about
> the ground force and skid length.
>
> What was your take on this question, Sarma?
>
> Brian W
>
> At 06:38 PM 1/7/2004, you wrote:
> >Thanks to all who have responded.
> >
> >regards,
> >Sarma.


Brian Whatcott Altus OK Eureka!