Energy. Energy cannot be created or destroyed
A force is described by its MAGNITUDE and by the direction in which it acts
Answer:
the maximum shear stress in the bar = 9.55 MPa
the twisting angle = 
Explanation:
From the diagram below;
Torque (T) = 2 kN × 5 mm + 2 kN × 5 mm
= 
= 200 N.m
Now; If we divide the shaft into two parts AC & BC
Then :
------------ equation (1)
At the junction :


⇒ 


replace
into above equation (1)

Again:

Now ; we can deduce that the maximum shear comes from
since 
So;

where;
R = 20 mm
D = 40 mm = 0.04 m
Then;


Thus ; the maximum shear stress in the bar = 9.55 MPa
b)
Again: 



Thus, the twisting angle = 
Answer:
The speed of the center of mass of the two carts is 0.103 m/s
Explanation:
It is given that,
Mass of the air track cart, m₁ = 350 g = 0.35 kg
Velocity of air track cart, v₁ = 1.25 m/s
Mass of cart, m₂ = 280 g = 0.28 kg
Velocity of cart, v₂ = -1.33 m/s (it is travelling in opposite direction)
We need to find the speed of the center of mass of the two carts. It is given by the following relation as :


Hence, this is the required solution.