Tag: physics

Questions Related to physics

Co-efficient of restitution is zero in

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

  1. Perfectly Inelastic collision

  2. Perfectly elastic collision

  3. Both A and B

  4. None

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Correct Option: A
Explanation:

In a perfectly inelastic collision having zero coefficient of restitution as the colliding particles stick together.

Line which is common normal for surfaces in contact during impact is known as

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

  1. Line of impact

  2. Line of collision

  3. Line of energy

  4. None

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Correct Option: A
Explanation:

Line which is common normal for surfaces  in contact during impact is known as line of impact. This is the line along which internal force of collision acts during impact.

How much force is exerted on a gunner by the machine gun, when the gunner fires machine gun, and $500$ bullets per minute are fired . The mass of bullet is $10g$ and it moves at $400\ m/s$ so as to avoid recoil.

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

  1. $\dfrac{100}{3}N$

  2. $200N$

  3. $2000N$

  4. $1000N$

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Correct Option: A

A ball of  mass $0.2kg$ is thrown against the wall$,$ the ball strikes the wall normally with velocity of $30m/s$ sand rebounds with velocity of $20m/s.$ Calculate the impulse of the force exerted by the ball on the wall

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

  1. $2N$

  2. $-10N$

  3. $20N$

  4. $40N$

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Correct Option: B
Explanation:

Given $, u = 30 m/s$ $, v = 20 m/s$ 

$m =  0.2 kg$
impulse $-$ change in momentum of the body$,$
$= mv - mu = m (v - u )$
$= 0.2 ( -20 -30 ) = -10 N$
Hence,
option $(B)$ is correct answer.

If a cricket ball hits you, it will hurt much more than a tennis ball would when moving with the same velocity because:

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

  1. a cricket ball is bigger

  2. a cricket ball has more mass

  3. a cricket ball has less density

  4. none of the above

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Correct Option: B
Explanation:

Impulse "Ft" is defined as change in momentum.

The ball with more momentum will hurt more. Here, cricket ball will hurt more as it has more momentum (mv) than tennis ball.
This is because cricket ball has more mass and same velocity as that of tennis ball.
So option B is correct.

Two solid rubber balls $A$ and $B$ having masses $200$ grams and $400$ grams are moving in opposite directions with velocity of $A$ equal to $0.3   {m}/{s}$. After collision the two balls come to rest, then the velocity of $B$ is

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

  1. $0.15 {m}/{s}$

  2. $1.5 {m}/{s}$

  3. $- 0.15 {m}/{s}$

  4. None

Show answer
Correct Option: C
Explanation:

Initial linear momentum of system $= {m} _{A} \bar { { V } _{ A } } + {m} _{B} \bar { { V } _{ B } }$
                                                      $ = 0.2 \times 0.3 + 0.4 \times {V} _{B}$
Finally both balls come to rest.
Finally linear momentum $= 0$
By the law of conservation of linear momentum.
$0.2 \times 0.3 + 0.4 \times {V} _{B} = 0$
${V} _{B} = -\dfrac{0.2 \times 0.3}{0.4} = -0.15  {m}/{s}$

A shell of mass $m$ moving with velocity $V$ suddenly breaks into $2$ pieces. The part having mass ${m}/{4}$ remains stationary. The velocity of the other shell will be:

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

  1. $V$

  2. $2V$

  3. ${3}/{4} V$

  4. ${4}/{3} V$

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Correct Option: D
Explanation:
Mass of the one part which remains at rest is $\dfrac{m}{4}$.
Thus mass of other shell is $\dfrac{3m}{4}$.
Using conservation of linear momentum :  $P _{initial} = P _{final}$
$m V = \dfrac{m}{4} \times 0 + \dfrac{3m}{4} V _2$
Or  $m V =   \dfrac{3m}{4} V _2$
$\implies$ $V _2 = \dfrac{4V}{3}$

Two bodies having same mass $40   kg$ are moving in opposite directions, one with a velocity of $10  {m}/{s}$ and the other with $7   {m}/{s}$. If they collide and move as one body, the velocity of the combination is

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

  1. $10 {m}/{s}$

  2. $7 {m}/{s}$

  3. $3 {m}/{s}$

  4. $1.5 {m}/{s}$

Show answer
Correct Option: D
Explanation:

By the conservation of momentum
   $40 \times 10 + \left(40\right) \times \left(-7\right) = 80 \times V$
   $V = 1.5   {m}/{s}$

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.