# Homework Help: Need Help on Forces

1. Oct 3, 2005

### chriszollman

I have a worksheet I recieved for make-up since I was absent. It is really hard since I miss the lesson. All the problems are similar, but I do no know where to start. Here is a sample problem. Will someone show me steps on how to do it?

A boat moves through the water with two forces acting on it. One is a 2.1 103 N forward push by the motor, and the other is a 1.9 103 N resistive force due to the water.
(a) What is the acceleration of the 1200 kg boat?
m/s2
(b) If it starts from rest, how far will it move in 10 s?
m
(c) What will its velocity be at the end of this time interval?
m/s

2. Oct 3, 2005

### hotvette

You need the basic equation of motion for an object:

$$\Sigma F_i = m a_i$$

In other words, in each coordinate direction, the sum of forces on an object is equal to the mass of the object times acceleration (i.e. second derivative of x with respect to t). Integrate twice to get x(t), evaluate the initial conditions from the problem statement, then solve from there.

3. Oct 3, 2005

### chriszollman

so would it be 200 N = 1200kg X A. v I tried that and i was told i was wrong.

4. Oct 3, 2005

### chriszollman

2.1 x 10^3 1.9x10^3 so 2100 n 1900 s0 2100-1900= 200??

5. Oct 3, 2005

### Staff: Mentor

I figured out what you meant. Yes: The net force is 200 N and the acceleration will be given via Newton's law, just like you wrote in post #3.