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1. sorry if this is in the wrong place, having a complete mental block.

A ball hits a wall horizontally at 6.0 m/s. It rebounds horizontally at 4.4 m/s. The ball is in contact with the wall for 0.040 s. What is the acceleration of the ball?

could someone try explain this to me and work through it with me. On msn if thats any easier (:

thanks
2. (Original post by ameliesmith)
sorry if this is in the wrong place, having a complete mental block.

A ball hits a wall horizontally at 6.0 m/s. It rebounds horizontally at 4.4 m/s. The ball is in contact with the wall for 0.040 s. What is the acceleration of the ball?

could someone try explain this to me and work through it with me. On msn if thats any easier (:

thanks
Acceleration is the change in velocity divided by the time taken.

For example, if a car is travelling at 30m/s and then, over ten seconds, accelerates to 40m/s, we can see that

Acceleration = change in velocity / time taken

= 10 / 10

= 1 m/s^2.

Now, in our example there is a 'trick' - when the ball rebounds off the wall, it is travelling in the opposite direction, so the velocity change is 6+4.4 = 10.4m/s , and not the 1.6m/s you might have first thought.

3. (Original post by M_E_X)
Acceleration is the change in velocity divided by the time taken.

For example, if a car is travelling at 30m/s and then, over ten seconds, accelerates to 40m/s, we can see that

Acceleration = change in velocity / time taken

= 10 / 10

= 1 m/s^2.

Now, in our example there is a 'trick' - when the ball rebounds off the wall, it is travelling in the opposite direction, so the velocity change is 6+4.4 = 10.4m/s , and not the 1.6m/s you might have first thought.

thanks

so basically you have to assume that the 4.4 m/s is negative as its going in the other direction then the whole minius, minus a minus is addition.

(6.0 - -4.4)/0.040 = 260 m/s/s

is this right?
4. (Original post by ameliesmith)
thanks

so basically you have to assume that the 4.4 m/s is negative as its going in the other direction then the whole minius, minus a minus is addition.

(6.0 - -4.4)/0.040 = 260 m/s/s

is this right?
Looks good to me

If you're replying to someone on here, you should usually quote them (click the 'quote' button to the bottom right of their post), then they get a notification you've replied - I just saw your post here by chance and could have missed it otherwise!

You have to really watch out for when velocities are negative or when they are positive, it's a common trick!
5. (Original post by M_E_X)
Looks good to me

If you're replying to someone on here, you should usually quote them (click the 'quote' button to the bottom right of their post), then they get a notification you've replied - I just saw your post here by chance and could have missed it otherwise!

You have to really watch out for when velocities are negative or when they are positive, it's a common trick!
yeah thanks for all your help!

it just seems like 260m/s/s is quite hight for the acceleration of the ball haha, 40m/s/s seem much more reasonalble
6. (Original post by ameliesmith)
yeah thanks for all your help!

it just seems like 260m/s/s is quite hight for the acceleration of the ball haha, 40m/s/s seem much more reasonalble
The 260m/s^2 answer is a correct. For a short discussion of why, here is a similar problem:

http://www.physicsforums.com/archive.../t-337573.html

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