# Homework Help: Forces and Motions

1. Sep 12, 2006

### Mono182

i'm really stuck on this problem:

A Hockey puck rebounds from a board as shown in Figure 16. The puck is in contact with the board for 2.5 ms. Determine the average acceleration of the puck ober the interval
http://img183.imageshack.us/img183/6277/untitled1copyfw2.jpg [Broken]

Last edited by a moderator: May 2, 2017
2. Sep 13, 2006

### Tomsk

Hi, you need to post your thoughts first. Hint- think about the components of the velocities in the north and east directions.

3. Sep 13, 2006

### Mono182

ya thats what i can't figure out. I have a hard time seeing the 2 dimensional problems. Since the velocity decreased 5 m/s, i tried a = (5m/s)/(0.0025s) to get the acceleration. that answer was wrong and the correct had a direction, [7.5º N of W]. I tried working backwards from the answer by plugging in the answer in a = v/t so i could see how to solve 2 dimensional problems; i concluded that V = -18.25 m/s over the time interval. Unfontunatley it didn't help me and i still can't see how to solve the problem.

4. Sep 13, 2006

### Tomsk

What you need to do is figure out the acceleration in the north direction, and also in the east direction. Use trig to find the components of the velocity in each of these directions. Then you can find both components of the acceleration. Then use trig to find the angle, by theta=tan(north component/east component).

5. Sep 13, 2006

### Mono182

wow, that was a great help. do you have any tips to how to go about solving 2D questions? thats my major problem, i can't seem to figure out how to start.

https://www.physicsforums.com/showthread.php?t=131772" those are other problems i don' t know how to start.

Last edited by a moderator: Apr 22, 2017