Speed is the rate of change <span>of distance.</span>
Explanation:
Given that,
Length of each rod, L = 15 m
Area of cross section of the rod, 
Young's modulus for steel, 
Total weight of two people, F = 1900 N
We need to find the stretching in the rod when the ride is at rest. The formula of Young's modulus of a material is given by :

Here,
is the stretching in the rod

So, the rod will stretched to 
Answer: Weight will remain same as on the Earth
Explanation :
From Universal law of gravitation :
......(1)
is the mass of earth
m is the mass of the person
R is the radius of the earth
We know that F= mg.....(2)
So, from equation (1) and (2)

.....(3)
It is given that, If we stood on a planet having a mass four times that of earth mass and a radius two times of earth radius then from equation (3)

The value of g is will not change. So, our weight would not change. It would remain the same as on the Earth.
Answer:
α = 68.8 rad/s²
Explanation:
Given: m = 13.5 kg r= 0.155 m radius.
Inertia is given by I = ½mr²
I = ½*13.5kg*(0.155m)²
I = 0.162 kg*m²
Given: m = 2.05kg ring inside radius ri= 0.18 m; outside radius ro= 0.32 m
I = ½m*(r₁² + r₂²)
I = ½*2.05kg*(0.18² + 0.32²)
I = 0.138 kg*m²
Tread: m = 9.5 kg r= 0.31 m
I = mr² (hoop/ring or cylindrical shell formula)
I = 9.5kg*0.31m²
I = 0.9129kg*m²
Drive shaft: m= 31 kg solid cylinder r = 3.1 cm = 0.031m.
I = ½mr²
I = 31kg*0.031m²
I = 0.0298 kg*m²
Total moment of intertia
I = 0.162 + 0.1.38 + 0.9129 + 0.0298
It = 1.2427 kg*m²
τ = α*2*I ,τ = 95%*180N= 171N
α = τ/2*I
α = 171N/2*1.2427
α = 68.8 rad/s²