Question

A ball moving with velocity $$2\,m{s^{ - 1}}$$  collides head on with another stationary ball of double the mass. If the coefficient of restitution is 0.5, then their velocities (in $$m{s^{ - 1}}$$ ) after collision will be

A. 0, 1  
B. 1, 1
C. 1, 0.5
D. 0, 2
Answer :   0, 1
Solution :
If two bodies collide head on with coefficient of restitution
$$e = \frac{{{v_2} - {v_1}}}{{{u_1} - {u_2}}}\,......\left( {\text{i}} \right)$$
From, the law of conservation of linear momentum
$$\eqalign{ & {m_1}{u_1} + {m_2}{u_2} = {m_1}{v_1} + {m_2}{v_2} \cr & \Rightarrow {v_1} = \left[ {\frac{{{m_1} - e{m_2}}}{{{m_1} + {m_2}}}} \right]{u_1} + \left[ {\frac{{\left( {1 + e} \right){m_2}}}{{{m_1} + {m_2}}}} \right]{u_2} \cr & {\text{Substituting }}{u_1} = 2\,m{s^{ - 1}},{u_2} = 0,{m_1} = m\,{\text{and}}\,{m_2} = 2m,\,e = 0.5 \cr} $$
we get, $${v_1} = \left[ {\frac{{m - m}}{{m + 2m}}} \right] \times 2$$
$$ \Rightarrow {v_1} = 0$$
Similarly, $${v_2} = \left[ {\frac{{\left( {1 + e} \right){m_1}}}{{{m_1} + {m_2}}}} \right]{u_1} + \left[ {\frac{{{m_1} - e{m_1}}}{{{m_1} + {m_2}}}} \right]{u_2}$$
$$\eqalign{ & = \left[ {\frac{{1.5 \times m}}{{3m}}} \right] \times 2 \cr & = 1\,m{s^{ - 1}} \cr} $$

Releted MCQ Question on
Basic Physics >> Momentum

Releted Question 1

Two particles of masses $${m_1}$$ and $${m_2}$$ in projectile motion have velocities $${{\vec v}_1}$$ and $${{\vec v}_2}$$ respectively at time $$t = 0.$$  They collide at time $${t_0.}$$ Their velocities become $${{\vec v}_1}'$$ and $${{\vec v}_2}'$$ at time $$2{t_0}$$ while still moving in the air. The value of $$\left| {\left( {{m_1}{{\vec v}_1}' + {m_2}{{\vec v}_2}'} \right) - \left( {{m_1}{{\vec v}_1} + {m_2}{{\vec v}_2}} \right)} \right|$$        is

A. zero
B. $$\left( {{m_1} + {m_2}} \right)g{t_0}$$
C. $$\frac{1}{2}\left( {{m_1} + {m_2}} \right)g{t_0}$$
D. $$2\left( {{m_1} + {m_2}} \right)g{t_0}$$
Releted Question 2

Two blocks of masses $$10kg$$  and $$4kg$$  are connected by a spring of negligible mass and placed on a frictionless horizontal surface. An impulse gives a velocity of $$14 m/s$$  to the heavier block in the direction of the lighter block. The velocity of the centre of mass is

A. $$30 m/s$$
B. $$20 m/s$$
C. $$10 m/s$$
D. $$5 m/s$$
Releted Question 3

A ball of mass $$0.2kg$$  rests on a vertical post of height $$5m.$$  A bullet of mass $$0.01kg,$$  traveling with a velocity $$V m/s$$  in a horizontal direction, hits the centre of the ball. After the collision, the ball and bullet travel independently. The ball hits the ground at a distance of $$20m$$  and the bullet at a distance of $$100m$$  from the foot of the post. The velocity $$V$$ of the bullet is
Momentum mcq question image

A. $$250 m/s$$
B. $$250\sqrt 2 \,m/s$$
C. $$400 m/s$$
D. $$500 m/s$$
Releted Question 4

A particle of mass $$m$$ is projected from the ground with an initial speed $${u_0}$$ at an angle $$\alpha $$ with the horizontal. At the highest point of its trajectory, it makes a completely inelastic collision with another identical particle, which was thrown vertically upward from the ground with the same initial speed $${u_0}.$$ The angle that the composite system makes with the horizontal immediately after the collision is

A. $$\frac{\pi }{4}$$
B. $$\frac{\pi }{4} + \alpha $$
C. $$\frac{\pi }{2} - \alpha $$
D. $$\frac{\pi }{2}$$

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