Find the components of the force

Gold Member
I know the answers to these problems but I'm having trouble obtaining them:

1)To model a spacecraft, a toy rocket engine is securely fastened to a large hockey puck, which can glide with negligible friction over a horizontal surface, taken as the xy plane. The 4.0 kg puck has a velocity of $300\hat{x}$m/s at one instant. 8 seconds later, it is to have a velocity of $v=(800\hat{x}+10\hat{y})m/s$. Assuming the rocket engine exerts a constant horizontal force, find
a) the components of the force
b)its magnitude

If someone could just show me how to set up part (a) I can easily go from there.

2) The distance between 2 telephone poles is 50m. When a 1.0 kg bird lands on the wire midway between the poles, the wire sags 0.2m. How much tension does the bird produce in the wire? (ignore the weight of the wire)

This one seems easy, but the answer is 613N and I can't seem to get that.

Any quick help is much appreciated!!