Tag: mechanics

Questions Related to mechanics

Two equal masses ${m} _{1}$ and ${m} _{2}$ moving along the same straight line with velocities $+3  {m}/{s}$ and $-5  {m}/{s}$ respectively collide elastically. Their velocities after the collision will be respectively :

force exerted by collision collisions work, energy and power mechanics physics

  1. $+4 {m}/{s}$ for both

  2. $-3 {m}/{s}$ and $+5 {m}/{s}$

  3. $-4 {m}/{s}$ and $+4 {m}/{s}$

  4. $-5 {m}/{s}$ and $+3 {m}/{s}$

Show answer
Correct Option: D
Explanation:

As ${m} _{1} = {m} _{2}$, therefore after elastic collision velocities of masses gets interchanged.

A machine gun of mass 5 kg fires 30 bullets, each of mass 50 g, per minute at a speed of $400\,m\,{s^{ - 1}}$. What force must be exerted to keep the machine gun in position?

force exerted by collision collisions work, energy and power mechanics physics

  1. $30N$

  2. $10N$

  3. $27N$

  4. $33N$

Show answer
Correct Option: B
Explanation:

Mass of the gun $=5kg$

Mass of bullets $=50g$
speed at which the bullet is fired$=400m/s$
Therefore$,$ force required to keep the machine gun in position $=\frac{{ch\arg e\,in\,momentum\,of\,bullets}}{{time\,taken}}$
$=\frac{{\left( {50 \times {{10}^{ - 3}} \times 30} \right) \times 400}}{{60}} = 10\,N$
Hence,
option $(B)$ is correct answer.

What happens when two forces in the same direction, are applied on an object?

physics mechanics concept of force and its unit force - push or pull forces

  1. Forces add up.

  2. Forces subtract.

  3. Resultant force is the division of forces.

  4. None of the above.

Show answer
Correct Option: A
Explanation:

When two forces are applied on a object in the same direction, forces added up and net force increases.

When you and your friend push a table in opposite directions, it becomes difficult to move. This is because:

physics mechanics concept of force and its unit force - push or pull forces

  1. the net force becomes the sum of  the two forces.

  2. the net force becomes the difference of the two forces.

  3. the table becomes heavier.

  4. the table becomes lighter.

Show answer
Correct Option: B
Explanation:

When two forces are applied in opposite directions, the net force becomes the difference of the two. So, the net force becomes small and the table becomes difficult to move.

Fill in the blanks:

The SI unit of force is _______.

physics mechanics concept of force and its unit force - push or pull forces

  1. Pascal

  2. Kelvin

  3. Newton

  4. Celcius

Show answer
Correct Option: C
Explanation:

In SI system of units, force is expressed in Newtons ($N$).

In the game of tug-of-war, the team that pulls the rope harder wins the game. This is because:

physics mechanics concept of force and its unit force - push or pull forces

  1. the rope moves in the direction of larger force.

  2. the rope moves in the direction of the smaller force.

  3. the rope does not move at all.

  4. the rope moves in the direction of product of the forces.

Show answer
Correct Option: A
Explanation:

In a game of tug-of-war, teams apply forces in terms of pulls on the rope. On the rope, two pulls act in opposite directions. The net force becomes the difference of the two forces (pulls) and the rope moves in the direction of the larger force (pull).

When you and your friend pushes heavy table in the same direction, it becomes easier to move. This is because:

physics mechanics concept of force and its unit force - push or pull forces

  1. the net force is the sum of forces.

  2. the net force is the difference of forces.

  3. the table becomes lighter.

  4. friction reduces.

Show answer
Correct Option: A
Explanation:

When you and your friend pushes heavy table in the same direction, the force applied by you and your friend get added. So, applied forces sum up to get a larger force. Hence the table moves easily.

What happens when two forces are applied in the opposite direction on an object?

physics mechanics concept of force and its unit force - push or pull forces

  1. Net force is the addition of forces.

  2. Net force is the subtraction of forces.

  3. Net force is the division of forces.

  4. Net force is the multiplication of forces.

Show answer
Correct Option: B
Explanation:

When two forces are applied in the opposition direction on an object, the net force will be the difference between the two forces.

A particle of mass $1\ g$ moving with a velocity $\vec {v _{1}} = 3\hat {i} - 2\hat {j} ms^{-1}$ experiences a perfectly in elastic collision with another particle of mass $2\ g$ and velocity $\vec {v _{2}} = 4\hat {j} - 6\hat {k} ms^{-1}$. The velocity of the particle is:

collisions in one dimension collisions work, energy and power mechanics physics

  1. $2.3\ ms^{-1}$

  2. $4.6\ ms^{-1}$

  3. $9.2\ ms^{-1}$

  4. $6\ ms^{-1}$

Show answer
Correct Option: B
Explanation:

From conservation of momentum
$m _{1}\vec {v _{1}} + m _{2}\vec {v _{2}} = (m _{1} + m _{2})\vec {v}$


$1\times (3\hat {i} - 2\hat {j}) + 2\times (4\hat {j} - 6\hat {k}) = (1 + 2)\vec {v}$

$\Rightarrow 3\hat {i} + 6\hat {j} - 12\hat {k} = 3\vec {v} $

$\Rightarrow \vec {v} = \hat {i} + 2\hat {j} - 4\hat {k}$


$v = |\vec {v}| = \sqrt {1 + 4 + 16} = 4.6\ ms^{-1}$.

A ball P moving with a speed of $v \ ms^{-1}$ collides directly with another identical ball Q moving with a speed $10\ ms^{-1}$ in the opposite direction. P comes to rest after the collision. If the coefficient of restitution is 0.6, the value of $v$ is:

collisions in one dimension collisions work, energy and power mechanics physics

  1. $30\ ms^{-1}$

  2. $40\ ms^{-1}$

  3. $50\ ms^{-1}$

  4. $60\ ms^{-1}$

Show answer
Correct Option: B
Explanation:


As momentum is conserved, we can say,

$m(v-10)=mv _2$

$v _2=(v-10)$

$e=\dfrac{v _2-v _1}{u _1+u _2}=\dfrac{(v-10)-0}{(v+10)}$

$0.6=\dfrac{v-10}{v+10}$

$0.6v+6=v-10$

$0.4v=16$ 

$v=40\ ms^{-1}$