A-Level Physics真题及答案解析

A Mangonel is a type of catapult used to launch projectiles such as rocks. A student made a working model of a Mangonel.

Mangonel是一种用来发射岩石的弹射器，下图是一个学生自制的弹射器。

As the handle is turned , the arm is pulled back by string. This increases the tension in the rubber band. When the string is released,the rubber band causes the arm to move upwards,launching a projectile from the bucket when the arm hits the crossbar.

(i)Suggest why a rubber band is used to support the arm.

请解释为什么要用橡皮筋作为支撑？

(ii)State the energy transfers that occur when the string is released. 

请说明当弦释放后发生了怎样的能量转化。

解析及参考答案

学生们可能没有听说过Mangonel（投石机），但是他们可以根据所学的物理知识回答问题。

所有须知的信息都在问题里了，题目完整描述了投石机的机臂是如何退后、启动、发射的。

这A题的答案在题目中基本已经给出来了：‘this increases the tension in the rubber band’. Therefore the rubber band acts to store elastic potential energy.

The answer to part (b) is based upon this and relies upon the student imagining the real life situation.

B题的答案基于上面提到的哪一点以及学生对于实际情况的想象。

Elastic potential energy in the rubber band is transferred to gravitational potential and kinetic energy as the projectile is fired upwards.