Stuntwoman Sherri \"Supergirl\" Thompson weighs 125 lb and is supposed to portra
ID: 1902778 • Letter: S
Question
Stuntwoman Sherri "Supergirl" Thompson weighs 125 lb and is supposed to portray the heroine in a new adventure film. During a chase sequence in an abandoned silver mine, Sherri must jump into an ore car at the top of a hill and try to escape from the mine by jumping over a ravine as shown in the figure below. Sherri climbs into the stationary ore car at point A and releases the brake to start the car rolling down the track. At point B she is supposed to use the brake to slow the car down because she sees a stationary ore car sitting on the track at point C. The brake that she is using will produce a constant 50 lbs of braking force (friction) parallel to the track. When Sherri's car hits the car at point C she will release the brake, the two cars couple and travel together until the track ends at point D. Sherri will stay with the two cars as they leave the track and hopefully fly over the ravine safely to the other side. The ore cars weigh 200 lbs each. Using the geometry below, Calculate the velocity of Sherri's car at point B Calculate the velocity of Sherri's car just before it impacts the stationary car at point C. Calculate the velocity of the coupled cars just after impact at point C. Calculate the velocity of the coupled cars just as they leave the end of the track at point D. Will Sherri and the cars make it over the ravine?Explanation / Answer
a)
(ms + mc) g * (80*0.3048) * sin40 = 0.5 (ms + mc) vi^2
==> g * 80*0.3048 * sin40 = 0.5 vi^2
==> 2 * 9.8 * 80*0.3048 * 0.642788 = vi^2
==> vi = 17.527 17.5 m/s
b)
0.5(ms+mc)vi^2+(ms+mc)g*(20*0.3048)*sin40-50*4.4482*(20*0.3048)=0.5(ms+mc)vf^2
==>
0.5*(125+200)*0.45359*17.527*17.527+(125+200)*0.45359*9.8*(20*0.3048)*0.642788-50*4.4482*(20*0.3048)
= (0.5*(125+200)*0.45359)*vf^2
vf = 19.1207 19.1 m/s