The spring in a retractable ballpoint pen is 1.8 cm long, with a 260 n/m spring constant. when the pen is retracted, the spring is compressed by 1.0 mm. when you click the button to extend the pen, you compress the spring by an additional 6.0 mm.
how much energy is required to extend the pen?

To solve this problem it is necessary to apply the concepts related to the elastic potential energy and the difference that can exist when there are two compression states.

By definition the potential elastic energy is defined as

Where

k = Spring constant

x = Displacement

In our case we have two displacements and compression states therefore

When 6 millimeters is compressed, from the first millimeter that was compressed we can define that from the initial state 7mm was compressed

The change in potential energy can then be expressed as

Replacing with our values

Therefore the total energy required is 0.00624J

i think the answer is a, hope this : )

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.