Tag: physics

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

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

  1. Line of impact

  2. Line of collision

  3. Line of energy

  4. None
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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.

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

  2. $200N$

  3. $2000N$

  4. $1000N$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Force = rate of change of momentum. Force = (n * m * v) / t, where n/t = 500 bullets/60 seconds. Force = (500/60) * 0.01 kg * 400 m/s = (50/6) * 4 = 200/3 N. Wait, the calculation is (500/60) * 0.01 * 400 = (50/6) * 4 = 200/3. Re-evaluating: 500 bullets/min = 500/60 bullets/sec = 25/3 bullets/sec. Force = (25/3) * 0.01 * 400 = (25/3) * 4 = 100/3 N.

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

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

  1. $2N$

  2. $-10N$

  3. $20N$

  4. $40N$
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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

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

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

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

  4. None
Reveal answer Fill a bubble to check yourself
C Correct answer
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.
$0.2 \times 0.3 + 0.4 \times {V} _{B} = 0$
${V} _{B} = -\dfrac{0.2 \times 0.3}{0.4} = -0.15  {m}/{s}$

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

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:

  1. $V$

  2. $2V$

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

  4. ${4}/{3} V$
Reveal answer Fill a bubble to check yourself
D Correct answer
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  $m V =   \dfrac{3m}{4} V _2$
$\implies$ $V _2 = \dfrac{4V}{3}$
Multiple choice force exerted by collision collisions work, energy and power mechanics physics

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

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

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

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

  4. $1.5 {m}/{s}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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

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

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 :

  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 $+3 {m}/{s}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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

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

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?

  1. $30N$

  2. $10N$

  3. $27N$

  4. $33N$
Reveal answer Fill a bubble to check yourself
B Correct answer
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.