Question

Two identical balls $$A$$ and $$B$$ moving with velocities $$+ 0.5\,m/s$$   and $$- 0.3\,m/s$$   respectively, collide head on elastically. The velocity of the balls $$A$$ and $$B$$ after collision will be respectively

A. $$ + 0.5\,m/s\,{\text{and}}\, + 0.3\,m/s$$
B. $$ - 0.3\,m/s\,{\text{and}}\, + 0.5\,m/s$$  
C. $$ + 0.3\,m/s\,{\text{and}}\,0.5\,m/s$$
D. $$ - 0.5\,m/s\,{\text{and}}\, + 0.3\,m/s$$
Answer :   $$ - 0.3\,m/s\,{\text{and}}\, + 0.5\,m/s$$
Solution :
When two bodies of equal masses undergo head on elastic collision in one dimension their velocities are just interchanged.

Releted MCQ Question on
Basic Physics >> Work Energy and Power

Releted Question 1

If a machine is lubricated with oil-

A. the mechanical advantage of the machine increases.
B. the mechanical efficiency of the machine increases.
C. both its mechanical advantage and efficiency increase.
D. its efficiency increases, but its mechanical advantage decreases.
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Releted Question 2

Two masses of $$1 \,gm$$  and $$4 \,gm$$  are moving with equal kinetic energies. The ratio of the magnitudes of their linear momenta is-

A. $$4:1$$
B. $$\sqrt 2 :1$$
C. $$1:2$$
D. $$1:16$$
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Releted Question 3

A particle of mass $$m$$  is moving in a circular path of constant radius $$r$$  such that its centripetal acceleration $${a_c}$$  is varying with time $$t$$  as $${a_c} = {k^2}r{t^2}$$   where $$k$$  is a constant. The power delivered to the particles by the force acting on it is:

A. $$2\pi m{k^2}{r^2}t$$
B. $$m{k^2}{r^2}t$$
C. $$\frac{{\left( {m{k^4}{r^2}{t^5}} \right)}}{3}$$
D. Zero
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Releted Question 4

A spring of force-constant $$k$$  is cut into two pieces such that one piece is double the length of the other. Then the long piece will have a force-constant of-

A. $$\left( {\frac{2}{3}} \right)k$$
B. $$\left( {\frac{3}{2}} \right)k$$
C. $$3k$$
D. $$6k$$
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