# Homework Help: Submarine diving problem

1. Mar 1, 2005

### yoyo

A submarine of mass m is diving at a 45 degree angle which means that the submarine's propulsion system is generating constant thrust T in the direction of the given angle. Assume that the density of the submarine is d1 and the density of water is d2. Further, assume that there is no resistance to motion.

a) List the forces acting on the submarine and draw an appropriate diagram.
-I think the forces that are acting on the submarine is gravity, force normal,buoyancy, but i'm not sure of what other forces there may be.

b) Examine the forces that you listed and draw a conclusion about the trajectory of the submarine.
- Have no idea of what the trajectory due to the forces are. Can someone please explain?

c) Set up a coordinate system to describe the motion (the x-axis can be the surface of the ocean, the submarine's initial location can be put at the origin) Write down Newton's equations and solve them assuming that the submarine did not have any initial velocity.
- I understand how to setup the coordinate system, but having trouble with setting up Newton's equation and solving it.

d) Plot three trajectories of the submarine for the cases d1>d2, d1=d2, and d1<d2, Label each trajectory accordingly.
- i have very little experience with plotting trajectories...can somebody help?

Last edited: Mar 1, 2005
2. Mar 2, 2005

### HallsofIvy

Well, since you were told there is a thrust, T, don't you think you should include that? And what is "force normal"? Normal to what?
I see thrust, bouyancy, and gravity.

The submarine will accelerate in the direction of the net force (F= ma). Which direction do you think the net force is in?

Newton's equation IS F= ma. The reference to Newton's equationS means you want to use that for each of the x, y, z directions.

You will find that the trajectories are straight lines. What happens to bouyancy in each of the cases given?