In the movie Jurassic Park , there is a scene in which some members of the visit

Question

In the movie Jurassic Park, there is a scene in which some members of the visiting group are trapped in the kitchen with dinosaurs outside. The paleontologist is pressing against the center of the door, trying to keep out the dinosaurs on the other side. The botanist throws herself against the door at the edge near the hinge. A pivotal point in the film is that she cannot reach a gun on the floor because she is trying to hold the door closed. If the paleontologist is pressing at the center of the door, and the botanist is pressing at the edge about 2 cm from the hinge, estimate how far the paleontologist would have to relocate in order to have a greater effect on keeping the door closed than both of them pushing together have in their original positions. (This question is courtesy of Edward F. Redish. For more questions of this type, see www.physics.umd.edu/perg/.)
d = ? cm

Explanation / Answer

Let's assume that they push with the same force. Torque is the cross product of force and distance; in this case, just F d.
The two torques are
F (2 cm) + F ( 1/2 w )
where w is the width of the door.

Now paleontologist will have to relocate such that torque produces by him balances the previous torque.

F.d = 2F + 0.5wF

d = 2 + 0.5w

typical width of door is 90 cm

d = 47 (approx.)

Hence paleontologist will have to shift by 45 - 47 = - 2 cm

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