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boyakko [2]
3 years ago
14

A rifle of mass 2 kg is suspended by strings. The rifle fires a bullet of mass 0.01 kg at a speed of 200 m/s. The recoil velocit

y of the rifle is about ____.
(A) 0.001 m/s.
(B) 0.01 m/s.
(C) 0.1 m/s.
(D) 1 m/s
Physics
1 answer:
ozzi3 years ago
5 0

Answer:

option D  

Explanation:

given,

mass of the rifle,M = 2 Kg

mass of the bullet , m = 0.01 Kg

speed of the bullet, v = 200 m/s

recoil velocity ,v'= ?

initial velocity of bullet and rifle is zero.

using conservation of energy

Mu + m u' = M v'+ m v

0 + 0  = 2 x v' + 0.01 x 200

2 v' = -2

   v' = -1 m/s

negative sign represent the velocity of rifle is in opposite direction of bullet.

hence, the correct answer is option D  

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Copper is a metal commonly used for electrical wiring in houses. Which metal conducts electricity better than copper at 20°C?
jek_recluse [69]
The correct answer is silver metal.
Conductivity measures the ability of a material or a metal to transmit energy, conductivity may be electrical, thermal or acoustical conductivity. The most electrical conductive element is silver, followed by copper and Gold. Silver also has the highest thermal conductivity as compare to any element. However, copper and Gold are more often used in electrical applications since copper is less expensive and gold has a much higher corrosion resistance. 
6 0
3 years ago
A woman pushes an oak chest across an oak floor at a constant speed of 0.450 m/s. The chest has a mass of 40.0 kg, and the coeff
natima [27]

Answer:

A. 243 N

Explanation:

Friction is the force that opposes the relative motion between systems that are in contact.

This friction force that opposes the motion of the oak chest across the oak surface will be equal and opposite to that exerted by the woman.

First find the normal force which is the force that would point directly upwards to support weight of the block.

Normal force, N= mg where m is the mass of the chest and g is the acceleration due to gravity.

Given m=40 kg and g=9.80 m/s²

N force=40×9.80 =392N

Then find the force of friction which is given by the formula;

<em>F=μN where μ is friction coefficient for the  oak chest  and N is the normal force on the chest</em>

Given <em>μ</em>=0.620  and N force = 392 N then it will be;

F=0.620× 392 =243.04 N

Answer : 243 N

6 0
3 years ago
Block B is attached to a massless string of length L = 1 m and is free to rotate as a pendulum. The speed of block A after the c
Amanda [17]

Complete Question

The diagram for this question is shown on the first uploaded image

Answer:

The minimum velocity of A is  v_A= 4m/s

Explanation:

From the question we are told that

    The length of the string is  L = 1m

     The initial speed of block A is u_A

     The final speed of block A is  v_A = \frac{1}{2}u_A

      The initial speed of block B is u_B = 0

      The mass of block A  is  m_A = 7kg  gh

      The mass of block B is  m_B  = 2 kg

According to the principle of conservation of momentum

       m_A u_A + m_B u_B = m_Bv_B + m_A \frac{u_A}{2}

Since block B at initial is at rest

       m_A u_A  = m_Bv_B + m_A \frac{u_A}{2}

      m_A u_A  - m_A \frac{u_A}{2} = m_Bv_B

          m_A \frac{u_A}{2} = m_Bv_B

  making v_B the subject of the formula

             v_B =m_A \frac{u_A}{2 m_B}

Substituting values

               v_B =\frac{7 u_A}{4}  

This v__B is the velocity at bottom of the vertical circle just at the collision with mass A

Assuming that block B is swing through the vertical circle(shown on the second uploaded image ) with an angular velocity  of v__B' at  the top of the vertical circle  

 The angular centripetal acceleration  would be mathematically represented

                   a= \frac{v^2_{B}'}{L}

Note that  this acceleration would be toward the center of the circle

      Now the forces acting at the top of the circle can be represented mathematically as

         T + mg = m \frac{v^2_{B}'}{L}

    Where T is the tension on the string

  According to the law of energy conservation

The energy at  bottom of the vertical circle   =  The energy at the top of

                                                                                the vertical circle

   This can be mathematically represented as

                 \frac{1}{2} m(v_B)^2 = \frac{1}{2} mv^2_B' + mg 2L

From above  

                (T + mg) L = m v^2_{B}'

Substitute this into above equation

             \frac{1}{2} m(\frac{7 v_A}{4} )^2 = \frac{1}{2} (T + mg) L  + mg 2L  

             \frac{49 mv_A^2}{16}  = \frac{1}{2} (T + mg) L + mg 2L

          \frac{49 mv_A^2}{16}  = T + 5mgL

The  value of velocity of block A needed to cause B be to swing through a complete vertical circle is would be minimum when tension on the string due to the weight of B is  zero

        This is mathematically represented as

                      \frac{49 mv_A^2}{16}  = 5mgL

making  v_A the subject

            v_A = \sqrt{\frac{80mgL}{49m} }

substituting values

          v_A = \sqrt{\frac{80* 9.8 *1}{49} }

              v_A= 4m/s

     

6 0
3 years ago
True or False : All Eukaryotes have cell walls?
CaHeK987 [17]
False only some eukaryotes have cell wall like plants, fungi, and some bacteria.
6 0
3 years ago
Read 2 more answers
a wooden block has a mass of 1.2 kg, a specific heat of 710, and is at a temperature of 25*C. what is the block's final temperat
mash [69]

The final temperature of the block is 27.5^{\circ} C

Explanation:

The amount of thermal energy Q supplied to a substance is related to the increase in temperature of the substance, \Delta T, according to the equation

Q=mC_s \Delta T

where:

m is the mass of the substance

C_s is the specific heat capacity of the substance

In this problem, we have:

m = 1.2 kg is the mass of the block

Q = 2,130 J is the amount of energy supplied to the block

C_s = 710 J/kg^{\circ}C is the specific heat capacity of the block

Solving for \Delta T, we find the increase in temperature:

\Delta T = \frac{Q}{m C_s}=\frac{2130}{(1.2)(710)}=2.5^{\circ}C

And since the initial temperature was

T_i = 25^{\circ}C

The final temperature will be

T_f = T_i + \Delta T = 25+2.5=27.5^{\circ} C

Learn more about specific heat capacity:

brainly.com/question/3032746

brainly.com/question/4759369

#LearnwithBrainly

8 0
3 years ago
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