Expert: Bobby Soltani - 10/6/2005

Question
Hello,


My last two years of HS (11-12th grade) will be home school for me. And my Physical Science courses came, I was cool until I saw Physics! I'm So confused could you help!

How do you calculate the acceleration of an object?

I'm thinking its simply multiplication, but I'm not sure. When it come to these types of problems what does the time (for this problem its 2 seconds) plays in getting the correct answer?

Ok heres the problem:

A player uses a hockey stick to increase the speed of a 0.200 kg hockey puck by 6 m\s in 2 seconds.

(a) How much did the hockey puck accelerate?
(b) How much Force was exerted on the puck?
(c) How much Force did the puck exert on the hockey puck?

Here's how I answered: 0.200
                      x 6
Equals: 1.200

Is there any subtraction of the seconds, like once I multiply, do I subtract the 2 seconds from my answer?

You have a great pic up by the way: ;)

Thanks So Much!
Jess

Answer
Hi Jessica,

Here are some equations you need to solve this problem.

Force equals mass times acceleration
F = ma

acceleration is equal to the change in velocity in a specified time.  For instance, if you went from 0 mph to 20 mph in 1 second, your acceleration would be the change in velocity (20 - 0 = 20 mph) divided by the number of seconds (1 second), which equals 20 mph/s.

We are given that the puck's velocity change 6 m/s in 2 seconds, so its acceleration was (6 m/s) divided by 2 sec which is 3 m/(s^2).

That is the answer for part a.

Part b.
F = ma = 0.200kg*3m/s^2 = 0.6 kg-m/s^2
since 1 Newton = 1 kg-m/s^2, the answer is 0.6 N

Part c.
Newtons laws say that given an interaction between two bodies, A & B, the force by A upon B equals that by B upon A.  Newton's third law.
Therefore the answer in c is the same as the answer in b.

I hope this helps you understand the problem.  Let me know if you have any questions.

Bobby