The formula v=fλ can be used here.
326=2500*λ
Note the 2500 as 2.5kHz is 2.5 thousand Hz.
λ = 326/2500
= 0.1304m = 0.130m
Gravity causes falling objects to accelerate.
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ANSWER:
250 J
STEP-BY-STEP EXPLANATION:
F = 20N is required to stretch the spring by 4 meters
We know that the force is equal to:

We solve for k (spring constant):

The work done in stretching the spring is given by the following equation (in this case the stretch is 10 meters:

The work required is 250 joules.