Compute the energy stored in a catapult made of two identical strips of rubber, each of original length of 20cm and cross-section area of 1.7×10^-4. The catapult is stretched 20cm to fire a stone of mass of 0.25kg. (The young's modulus for the rubber is 5×10^6)

Question

Compute the energy stored in a catapult made of two identical strips of rubber, each of original length of 20cm and cross-section area of 1.7×10^-4. The catapult is stretched 20cm to fire a stone of mass of 0.25kg. 

 (The young's modulus for the rubber is 5×10^6)

Answer 1

L₀ = 20 × 10^-2 m

ΔL = 20 × 10^-2 m 

A = 1.7 × 10^-8 m² 

Y = 5 × 10⁶ N/m²

Now, 

E = FL₀ 

The young modulus is given by:- 

Y = FL₀ / AΔL

FL₀ = Y× AΔL

FL₀ = 5 × 10⁶ × 1.7 × 10^-8 × 20 × 10^-2 = 170 × 10^-4 = 0.17J

E = 0.17J 

The energy stored in catapult is 0.17J