Question

A particle moves in the $$X$$ - $$Y$$ plane under the influence of a force such that its linear momentum is $$\vec p\left( t \right) = A\left[ {\hat i\cos \left( {kt} \right) - \hat j\sin \left( {kt} \right)} \right],$$       where $$A$$ and $$k$$ are constants, The angle between the force and the momentum is

A. $${0^ \circ }$$
B. $${30^ \circ }$$
C. $${45^ \circ }$$
D. $${90^ \circ }$$  
Answer :   $${90^ \circ }$$
Solution :
$$\eqalign{ & \overrightarrow p \left( t \right) = A\left[ {\hat i\cos \left( {kt} \right) - \hat j\sin \left( {kt} \right)} \right] \cr & \overrightarrow F = \frac{{d\overrightarrow p }}{{dt}} = Ak\left[ { - \hat i\sin \left( {kt} \right) - \hat j\cos \left( {kt} \right)} \right] \cr & {\text{Here,}}\,\,\overrightarrow F .\overrightarrow P = 0\,\,{\text{But}}\,\,\overrightarrow F .\overrightarrow p = Fp\cos \theta \cr & \therefore \cos \theta = 0 \Rightarrow \theta = {90^ \circ }. \cr} $$

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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