M2 Particle Kinematics - Please Help!

I don't understand why my reasoning for part (b) of this question is incorrect.


You're given a function which represents the y displacement using the x displacement. You're then given a displacement of x, meaning that you can then find the y displacement at the point x = 20. I'm completely failing to see where I've gone wrong with this question - any help is greatly appreciated. Mark scheme is below:

You've determined the absolute position (x,y), not the direction of motion (dx,dy).
The direction of motion is the gradient of the curve.

As the model solution shows,
* calculate dy/dx
* evaulate at x = 20, this gives the gradient dy(20)/dx.
* they map the gradient to the angle using atan() to give the direction.

I don't understand why my reasoning for part (b) of this question is incorrect.


You're given a function which represents the y displacement using the x displacement. You're then given a displacement of x, meaning that you can then find the y displacement at the point x = 20. I'm completely failing to see where I've gone wrong with this question - any help is greatly appreciated. Mark scheme is below:

Give her a bit more help... she is almost there,