(1) When exploring the plane mirror imaging experiment, the transparent glass plate is used instead of the plane mirror, which is convenient for determining the image position;

(2) The included angle between the reflected light and the normal is the reflection angle; According to the optical path diagram shown in (a), the reflection angle is 60 degrees;

(3) There are five cells between 65438 and 0n on the spring dynamometer, so one cell represents 0.2N, that is, the scale value of this spring dynamometer is 0.2n, and the pointer is "2.4" at this time, so the weight of the object is 2.4n. 。

So the answer is: (1) glass plate; (2)60; (3)0.2; (4)3.6.