Question

1. When a rubber strip with a 3 by 1.5 mm cross section is suspended vertically and various masses are attached to it, a student obtains the following data for length versus load.

   Load (g):           0       100     200    300    400    500

Length (cm):    5.0      5.6      6.2     6.9     7.8    10.0

1. Find Young’s modulus for the rubber strip for small loads.
2. Find the energy stored in the strip when the load is 150 g. (Hint the energy can be given by U = (1/2) FΔL where F = force and ΔL is change in length)

Answer 1

a)

Young's Modulus is given by,   OR   

Here,

Smallest Force applied is of 100 g Force,    

Area of Cross section,  

Original length ( no load length),  

Elongation for smallest load,

Substituting,  

b)

150 g Force,   

We have the deflection for 100 g and 200 g as 5.6 cm and 6.2 respectively. Since 150g is the average, Deflection is also its average,

Energy stored,   

Substituting,