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Unformatted text preview: ach the elephant? Assume the dart's trajectory is nearly horizontal. = Prob~m ~ = 56. A meteorite strikes Earth and embeds itself 1.7 m into the ground. Scientists dig up the'lmeteorite and find that its mass is 400 gj they ~~timate that the ground exerted a retarding force df 106 Non the meteorite. Estimate the impact s~eed of the meteorite. Solution Solution "
The average 106 N non-conservative frictiJnal retarding force acts over a distance of 1.7 fu opposite to the direction of penetration in stopping'i,the meteorite. If we neglect the (small) chang~i in potential energy during the penetration the work-erihgy theorem gives Wnc -(106 N)(1. 7 m) J.K + 11URf. 11K == 0 - !mv; -!(O.4 kg)v;, or Vi ~.92km/s.. (a) Assume that there is no change in the gravitational potential energy of the dart, and that the stoppingforee is the only non-negligible, non-conservative force. Then Wnc =-F(2.2 em) = 11U + 11K -ikx2 = -i(690 N/m)(0.14 m)2, or F =307 N. (b) The (horizontal) speed of the dart as it leaves the spring is v = &...
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