Answer:
200 N
Explanation:
Since Young's modulus for the metal, E = σ/ε where σ = stress = F/A where F = force on metal and A = cross-sectional area, and ε = strain = e/L where e = extension of metal = change in length and L = length of metal wire.
So, E = σ/ε = FL/eA
Now, since at break extension = e.
So making e subject of the formula, we have
e = FL/EA = FL/Eπr² where r = radius of metal wire
Now, when the radius and length are doubled, we have our extension as e' = F'L'/Eπr'² where F' = new force on metal wire, L' = new length = 2L and r' = new radius = 2r
So, e' = F'(2L)/Eπ(2r)²
e' = 2F'L/4Eπr²
e' = F'L/2Eπr²
Since at breakage, both extensions are the same, e = e'
So, FL/Eπr² = F'L/2Eπr²
F = F'/2
F' = 2F
Since F = 100 N,
F' = 2 × 100 N = 200 N
So, If the radius and length of the wire were both doubled then it would break when the tension reached 200 Newtons.
Average speed = total distance / total time
total distance = 40 + 20 = 60km
total time taken = 10 + 5 = 15 minutes
Average speed = 60/15 = 4km/min
The answer is 2.49 x 10^5 KJ. This was obtained (1) use the formula for specific heat to achieve Q or heat then (2) get the energy to melt the copper lastly (3) Subtract both work and the total energy required to completely melt the copper bar is achieved.
