Answer:
a) KE = 888.26J
b) N = 294.5 turns
Explanation:
For the kinetic energy:

The inertia is:

So, the kinetic energy will be:

Now, friction force is:
Ff = μ*N = 0.80*5N = 4N
The energy balance would be:
Kf - Ko = Wf where Kf=0; Ko = 888.26J; and Wf is the work done by friction force.
Wf = -Ff*d = -Ff*N*2*π*R where N is the amount of turns it gives.
Replacing these values into the energy balance:
0-888.26=-4*N*2*π*0.12
-888.26=-0.96*π*N
N=294.5 turns
Explanation:
The magnetic needle of a compass lines up with Earth's magnetic poles.
Since Astronaut and wrench system is isolated in the space and there is no external force on it
So here momentum of the system will remain conserved
so here we can say

initially both are at rest
so here plug in all values


so here the astronaut will move in opposite direction and its speed will be equal to 0.20 m/s
Answer: 
Explanation:
Given
Current in the first wire 
Current in the second wire 
wires are
apart
Force per unit length between the current-carrying wires is

Force exerted by the wires is the same
Put the values

This force will be repulsive in nature as the current is flowing opposite
Answer:
a. Ssystem > 40 J/K
Explanation:
Given that
The entropy of first block = 10 J/K
The entropy of second block = 30 J/K
When two bodies come into contact with each other, the entropy of the combined system will increase and the entropy sum remains unchanged: According to the Second law of thermodynamics.The entropy of the system will be greater than 40 J/K.
Therefore the answer is a.
Ssystem > 40 J/K