For counting x you use simple equation for the distance covered by the object when it moves with constant velocity:

that gives you 20m after 1st second, 40 m after 2nd second, 60 m after 3rd second and so on.
For counting y you have to use the equation for the distanced covered by the object moving with constantly accelerating velocity (symbols refering to vertical movement):

that gives you 5m after 1st second, 20m afters 2nd second, 45m after 3rd second and so on.
Add minus signs before y positions to receive graph presenting the movement of the ball.
So the points are: P1=[20,-5], P2=[40,-20], P3=[60,-45] and so on... Pn=[x,y].
Energy cannot be created nor be destroyed
Answer:
Option D
0.83 m/s2
Explanation:
Time is assumed as 10 seconds
First, convert the speeds from km/h to m/s
20 km/h\times \frac {1000 m}{3600 s}=5.555555556 m/s
\approx 5.56 m/s
50 km/h\times \frac {1000 m}{3600 s}=13.88888889 m/s \approx 13.89 m/s
Acceleration,
where u and v are the initial and final velocities respectively, t is the time taken to accelerate.
Substituting 13.89 m/s for v, 5.56 m/s for u and 10 s for t then
