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1.

A neutron exerts a force on a proton which is(a) gravitational (b) electromagnetic(c) nuclear(d) weak.

Answer»

(a) gravitational
(c) nuclear

Explanation:

A neutron exerts both the gravitational and nuclear forces on a proton. 

The gravitational force can be seen between a neutron and a proton. However, its strength is negligible. The nuclear force is exerted only if the interacting particles are neutrons or protons or both. A neutron cannot exert electromagnetic force, because it is a neutral particle
Discussion
2.

Suppose the magnitude of nuclear forces between two protons varies with the distance between them as shown in figure (4-Q1). Estimate the ratio "Nuclear force/Coulomb force" for (a) x=8 fm (b) x=4 fm, (c) x=2 fm and (d) x=1 fm (1 fm =10-15 m).

Answer»

In the given figure force on the Y-axis is plotted on a logarithmic scale. Magnitude of Nuclear forces from the given figure by logarithmic interpolations are, 

For x=8 fm, => 0.18 N   

For x=4 fm, => 1.00 N    

For x=2 fm, => 17.7  N  

For x=1 fm, => 177 N  

Now Coulomb force is given by, F=q²/4π ε0 r²  = 9x109 .e²/r² = 9x109 .(1.6x10-19 )²/r². (10-15)2   = 144/r² N (Here r is in fm)   

So this force, 

for x=8 fm, => 2.25 N  

for x=4 fm, => 9.00 N  

for x=2 fm, => 36.00 N  

for x=1 fm, => 144.0 N    

So the ratio "Nuclear force/Coulomb force"    

(a) for x=8 fm is  0.18 N/2.25 N = 0.08  

(b) for x=4 fm is  1.0 N/9.0 N = 0.11   

(c) for x=2 fm is  17.7 N/36.0 N = 0.491  

(d) for x=1 fm is  177 N/144 N = 1.23   

It is clear that in the range of r< 2 fm Nuclear forces are quite comparable to Coulomb forces.
Discussion
3.

Action and reaction(a) act on two different objects(b) have equal magnitude(c) have opposite directions(d) have resultant zero.

Answer»

(a) act on two different objects
(b) have equal magnitude
(c) have opposite directions
(d) have resultant zero.

Explanation:

The two forces vector F and vector -F connected by Newton’s third law are known as action-reaction pair. For example, when a man jumps out from a ferry, he applied some force on the ferry. So, the action force in this case is the force applied by the man and the reaction is the force exerted by the ferry on the man. Both the forces act upon different objects (the man and the ferry) but have equal magnitudes and opposite directions. As a result, their resultant is zero.
Discussion