Question

Because of your physics background, you have been asked to be a stunt consultant for a motion picture about a genetically synthesized prehistoric creature that escapes from captivity and terrorizes the city. The scene you are asked to review has the three main characters of the movie being chased by the creature through an old warehouse. At the exit of the warehouse is a thick steel fire door 10 feet high and 6.0 feet wide weighing about 2000 pounds. In the scene, the three actors are to flee from the building and close the fire door (initially at rest), thus sealing the creature inside the building. With the creature running at 30 mph, they have 5.0 seconds to shut the door with a force of 50 pounds. When they push together, each actor needs a space of about 1.5 feet between them and the next actor. The door needs to rotate 120 degrees fore it to close completely.

Answer 1

The torque on the first person is, t,-6 feet The torque on the second person is, 2-(L-d) r2-(6-1.5)feet -4.5 feet The torque on the third person is, r, (6 -2x1.5)feet -3 feet The net torque is, T,, -(6+4.5+3)F (13.5 feet) F (13.5x0.3048 m)22.68 kg (13.5x0.3048 m)22.68xg N Thus, the net torque is, -(13.5x0.3048 m)22.68x(9.8 m/s) N -914.572 N-m The momentlof inertia of the door is 907.184 kg) (6x 0.3048 m) 1011.362 kg-m1

Calculate the angular acceleration as follows: "m-1α 914.572 N-m 1011.362 kg-m 0.9042 rad/s Now, calculate the time as follows: The value of θ is equal to 120and 120is equal to Hence, , , 2,7 (0.9042 rad/s*)t2 t 2.15s