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# Mechanics Question watch

1. (ok ive looked at the mark scheme and still dont get it. the answer is (-1.5i-1j) m/s How on earth do you calculate this?!?!)

An object has mass 8kg, and velocity of (3i -1j) m/s

The object collides with a smooth barrier which lies in the direction 0i +1j

The coefficient of restitution in the collision is 0.5.

Calculate the velocity of the object after impact.

2. Hey MathsNerd.
Now this is not as hard as you may think, just a little daunting on first glance. Now hopefully you have encountered collisions involving vectors before in class.

Now the thing to do with this is to break up the initial velocity of the object in to components parallel and perpendicular to the barrier, draw yourself a diagram and youll see that in actual fact it is very easy to break up 3i + (-1)j m/s in to perpendicular and parallel comonents to the barrier. As a little note, its sort of confusing what it means by the barrier lies in the direction 0i + 1j, bascially it is just a vertical barrier. Have a go at that then, applying you knowledge of how collisions work to the 'relevant' component(s).
3. oh i finally undersatnd now! it seems it was the barriers bit that was the bit i was confused about!! thanks alot, grats on oxford by the way! you deserve it!

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