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In outer space a rock whose mass is 3kg and whose velocity was(3900,-2900,3000)m/sstruck a rock with mass 13kg and velocity(220,-260,300)m/s. After the collision, the 3kg rock鈥檚 velocity is(3500,-2300,3500)m/s. (a) What is the 铿乶al velocity of the 13kg rock? (b) What is the change in the internal energy of the rocks? (c) Which of the following statements about Q (transfer of energy into the system because of a temperature difference between system and surroundings) are correct? (1)Q0 because the duration of the collision was very short. (2)Q=Ethermal of the rocks. (3)Q0 because there are no signi铿乧ant objects in the surroundings. (4)Q=k of the rocks.

Short Answer

Expert verified

(a)(312,-398,185)m/s

(b) 61.69106J

(c)(1)

Step by step solution

01

Identification of the given data

The given data is listed below as-

  • The mass of the first rock is,m1=3kg .
  • The velocity of the first rock is,V1i=(3900,-2900,3000)m/s
  • The mass of the second rock is,m2=13kg
  • The velocity of the second rock is,V2i=(220,-260,300)m/s
  • After the collision, the velocity of the first rock is,V1f=(3500,-2300,3500)m/s
02

Significance of the first law of thermodynamics, work-energy theorem, and law of conservation of momentum

The first law of thermodynamics states that the change in the internal energy of an object is equal to the difference between the energy transfer and the work done by the system.

The law of conservation of momentum states that the rate of a system before and after collision remains constant if no external force acts.

The work-energy theorem states that the net work done by the system is equal to the change in the system鈥檚 kinetic energy.

The law of conservation of momentum gives the final velocity of the second rock, and the work-energy theorem. The first law of thermodynamics gives the change in the internal energy of the rocks.

03

Determination of the final velocity of the second rock

The expression for the initial momentum of the system can be expressed as,

pinitial=(m2v2i)+(m1v1i)

Here,pinitialis the initial momentum of the systemm1andm2are the mass of the first and the second rock respectively andv1iandv2iare the initial velocities of the first and the second rock respectively.

For localid="1657877689140" m1=3kg,m2=13kg,v1i=(3900,-2900,3000)m/sandv2i=(220,-260,300)m/s.

Pinitial=(3kg)(3900,-2900,3000)m/s+(13kg)(220,-260,300)m/s=(11700,-8700,9000)kg,m/s+(2860,-3380,3900)kg,m/s=(14560,-12080,12900)kg.m/s

According to the law of conservation of momentum, the initial and the final rate of the system are the same. So, the final velocity of the system is expressed as,

Pfinal=(m1v1,i)+(m2v2,i)Pinitial=(m1v1,i)+(m2v2,i)

Here,v2,i is the final velocity of the second rock.

For Pinitial=14560,-12080,2900kg.m/s,m1=3kg,m2=13kgand v1,i=(3500,-2300,3500)m/s.

14560,-12080,12900kg.m/s=3kg3500,-2300,3500m/s+13kgv2,i=10500,-6900,10500kg.m/s+13(v2,i)kg4060,-5180,2400kg.m/s=13(v2,i)kgv2,i(312,-398,185)m/s

Thus, the final velocity of the13kg rock is(312,-398,185)m/s .

04

Determination of the change in the internal energy of the rocks

The magnitude of the initial velocity of the first rock is expressed as,

V1i=vx2+(vy)2+(vz)2

Here, vx,vyand vzare the initial velocities of the first rock at the x,yand zcoordinate respectively.

For Vx=3900m/s,Vy=-2900m/sand Vz=3000m/s.

V1i=39002+-29002+30002m/s=5711.39m/s

The magnitude of the initial velocity of the second rock is expressed as,

v2i=vx2+vy2+vz2

Here,vx,vyand vzare the initial velocities of the second rock at the x,yand zcoordinate respectively.

For vx=220m/s,vy=-260m/sand Vz=3000m/s.

v2i=2202+-2602+30002m/s=3019.27m/s

The magnitude of the final velocity of the first rock is expressed as,

V1i=vx2+(vy)2+(vz)2

Here, Vx,VYand Vzare the final velocities of the first rock at the x,yand zcoordinate respectively.

For vx=3500m/s,vy=-2300m/sand vz=3500m/s.

v1i=35002+-23002+35002m/s=5458.02m/s

The magnitude of the final velocity of the second rock is expressed as,

v2i=vx2+vy2+vz2

Here,role="math" localid="1657883192673" vx,vyand vzare the final velocities of the second rock at the x,yandzcoordinate respectively.

For vx=312m/s,vy=-398m/sandvz=185m/s.

v2i=3122+-3982+1852m/s=538.49m/s

From the first law of thermodynamics, the equation of the change in the internal energy of the rocks can be expressed as,

l=Q-W

Here, Q and W are the transfer of energy and work done by the system respectively.

For the first rock,

According to the work-energy theorem, the net change in the work done changes the system鈥檚 kinetic energy. So, the value is approximately Q as the duration of the collision is very short.

Hence, the equation of the change in the internal energy can be expressed as,

role="math" localid="1657885101892" l=0-(finalK.E,-initialK.E.)=initialK.E.-finalK.E. 鈥(1)

The equation of the total initial kinetic energy can be expressed as,

KEi=12m1v21i+12m1v22i

For m1=3kg,m2=13kg,v1i=5711.39m/sandv2i=3019.27m/s,

KEi=12(3kg)(5711.39m/s)2+12(13kg)(3019.27m/s)2=(1.5kg)(3.2107)m2/s2+(6.5kg)(9.1106)m2/s2=48.92106kg.m2/s2+59.25106kg.m2/s2=108.17106kg.m2/s21J1kg.m2/s2=108.17106J

The equation of the total final kinetic energy can be expressed as,

KEi=12m1v21i+12m2v22i

Form1=3kg,m2=13kg,v1i=5458.02m/s andv2,i=538.49m/s .

KEi=12(3kg)(5458.02m/s)2+12(13kg)(538.49m/s)2=(1.5kg)(2.9107)m2/s2+(6.5kg)2.8105m2/s2=44.68106kg.m2/s22+1.82106kg.m2/s2=46.68106kg.m2/s21J1kg.m2/s2=46.68106J

Substituting all the values in equation (1).

l=108.17106J-46.48106J=61.69106J

Thus, the change in the internal energy of the rocks is61.69106J .

05

Identification of the correct statement about internal energy

As it is assumed that the collision is short, the value of the is approximately 0.

Statement 2 saysQ=Ethermal for the rocks. However, this statement is incorrect as, during a short collision, the value cannot be high as theEthermal .

Statement 3 says the value is approximately zero as there are no significant objects in the surroundings. However, this statement is incorrect as the value is zero as the collision is short, not because of the surroundings.

Statement 4 saysQ=k that for the rocks. This statement is incorrect because the value is zero due to the short collision.

Statement 1 states thatQ0 as the collision is short. However, this statement is correct as the collision is fast with the rocks.

Thus, statement 1 is correct.

Thus, the duration of the collision was very short.

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