根据句意及首字母或者图片提示填空。
1. English isn't d_______ to learn, if you have an efficient method.
2. I like v_______ very much, for it is very fun.
3. Playing _______ is indeed really interesting. 
4. My sister has a ping-pong _______. 
5. _______ is young boys' favorite. 
6. We need a _______ ball, Dad! 
7. Does your sister have a _______? 
8. —Where is your pencil, Dave? —It's in the _______ on the desk. 
9. There are many _______ on the tree. 
10. His sister has two _______ They're very nice. 
的速度水平抛出，不计空气阻力。选地面为零重力势能面，当物体落到离地面高度为5m处时，物体的机械能和动能分别是( ) (g=10m/s2)