Question

Agent Bond is standing on a bridge, 13.5 m above the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s, which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this region. The roof of the truck is 3.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he drops down from the bridge onto the truck, making his getaway.
How many poles is it?

Answer 1

Answer:

Step-by-step explanation:

Eek!  Let's give this a go. Things we know:

acceleration of Bond in free fall is -9.8 m/s/s

velocity of the truck is 25 m/s

displacement Bond will travel when he jumps is -10 m

What we are looking for is the time it will take him to hit the top of the truck, knowing that the truck can travel from one pole to the next in 1 second.

Our displacement equation is

Δx = v₀t + 1/2at²

Filling in we have

$-10=25t+\frac{1}{2}(-9.8)t^2$

Simplifying we get

$-10=25t-4.9t^2$

This is a quadratic that needs to be solved however you personally solve quadratics.  When you do that, you find that the times it will take Bond to drop that displacement is either -.37 seconds or 5.47 seconds.  Many things in physics can be negative, like velocity and acceleration, but time NEVER will be.  So it takes Bond 5.5 seconds to drop to the roof of the moving truck.  That means that he needs to jump when the truck is between the 5th and the 6th poles away from him.

Good luck with this!

Cheers!