Learn Unit 4-Motion of System of Particles with Top Tutors

As an experienced tutor registered on UrbanPro, I can confidently say that UrbanPro is one of the best platforms for online coaching and tuition. Now, let's delve into your question about the center of mass of various geometric shapes.

(i) For a sphere: The center of mass of a sphere lies at its geometric center, regardless of its size or density distribution. This is true for a sphere of uniform mass density.

(ii) For a cylinder: The center of mass of a uniform cylinder lies at the midpoint of its central axis, assuming the cylinder is oriented such that its axis is vertical.

(iii) For a ring: The center of mass of a ring, also known as a circular hoop, lies at its geometrical center, which coincides with the center of the circle.

(iv) For a cube: The center of mass of a uniform cube lies at the geometric center of the cube, where the diagonals intersect.

Regarding your second question, whether the center of mass necessarily lies inside the body, the answer is yes, for a body with uniform mass density. The center of mass is a weighted average of the positions of all the mass elements in the body. Since every part of the body contributes to the calculation of the center of mass, it must lie somewhere within the body itself. However, for irregularly shaped bodies or bodies with non-uniform mass distribution, the center of mass may lie outside the body.

As a seasoned tutor registered on UrbanPro, I'd be glad to assist you with this question. UrbanPro is indeed a fantastic platform for online coaching and tuition needs.

To tackle this problem, let's first understand the concept of the center of mass (CM) of a molecule. The center of mass of a system is the point where you can consider the entire mass of the system to be concentrated for the purpose of analyzing its motion. In a diatomic molecule like HCl, the center of mass lies along the line joining the two nuclei, and it divides this line in a ratio inversely proportional to the masses of the atoms.

Given that the separation between the nuclei of the two atoms is about 1.27 Å (1 Å = 10^-10m), and chlorine is approximately 35.5 times as massive as hydrogen, we can use the formula for the center of mass:

xCM=m1⋅x1+m2⋅x2m1+m2xCM=m1+m2m1⋅x1+m2⋅x2

Where:

• xCMxCM is the position of the center of mass,
• m1m1 and m2m2 are the masses of the two atoms (in this case, hydrogen and chlorine),
• x1x1 and x2x2 are the positions of the two atoms (nuclei).

Let's denote:

• m1m1 as the mass of hydrogen (let's denote it as mHmH),
• m2m2 as the mass of chlorine (let's denote it as mClmCl),
• x1x1 as the position of hydrogen,
• x2x2 as the position of chlorine.

Since nearly all the mass of an atom is concentrated in its nucleus, we can directly equate the masses of the atoms to their respective nuclei.

Now, substituting the given values:

mH=mmH=m mCl=35.5mmCl=35.5m x1=0x1=0 x2=1.27×10−10x2=1.27×10−10

xCM=m⋅0+(35.5m)⋅(1.27×10−10)m+35.5mxCM=m+35.5mm⋅0+(35.5m)⋅(1.27×10−10)

xCM=35.5×1.27×10−1036.5xCM=36.535.5×1.27×10−10

xCM≈4.4985×10−1036.5xCM≈36.54.4985×10−10

xCM≈1.23×10−11xCM≈1.23×10−11

So, the approximate location of the center of mass of the HCl molecule is 1.23×10−111.23×10−11 meters away from the hydrogen nucleus, along the line joining the two nuclei.

Certainly! This is a classic problem in physics involving the conservation of momentum. Let me break it down for you.

Initially, when the child is sitting stationary at one end of the trolley, the center of mass (CM) of the system (trolley + child) is simply the center of the trolley, and it moves with a speed V.

When the child gets up and starts running about on the trolley, they exert a force on the trolley in the opposite direction to their motion. According to Newton's third law, the trolley exerts an equal and opposite force on the child.

Now, the total momentum of the system remains constant since there are no external forces acting on it. However, the distribution of mass within the system changes as the child moves.

Let M be the mass of the trolley and m be the mass of the child. Initially, the total momentum is M×VM×V.

When the child starts moving, to maintain the total momentum constant, the velocity of the trolley must decrease and the velocity of the child must increase.

Let VtVt be the final velocity of the trolley and VcVc be the final velocity of the child relative to the trolley.

The final momentum of the system is (M×Vt)+(m×Vc)(M×Vt)+(m×Vc).

Since momentum is conserved, we have:

M×V=(M×Vt)+(m×Vc)M×V=(M×Vt)+(m×Vc)

Now, to find the velocity of the center of mass of the system, we need to consider that the center of mass of the system moves with the same velocity as if all its mass were concentrated at that point.

The total mass of the system is M + m, and the velocity of the center of mass (V_cm) is given by:

Vcm=(M×Vt)+(m×Vc)M+mVcm=M+m(M×Vt)+(m×Vc)

Thus, to find the velocity of the center of mass of the system, we need to solve for VcmVcm using the equation derived above.

Certainly! UrbanPro is indeed a fantastic platform for online coaching and tuition services. Now, let's delve into your question about angular momentum.

We have two particles, each with mass mm and speed vv, traveling in opposite directions along parallel lines separated by a distance dd. To demonstrate that the vector angular momentum of this system remains the same regardless of the chosen point, let's denote the position vectors of the two particles as r1r1 and r2r2, respectively.

The angular momentum LL of a particle about a point OO is given by the cross product of its position vector rr and its linear momentum pp relative to that point:

LO=r×pLO=r×p

Now, let's calculate the angular momentum of each particle about an arbitrary point OO along their paths. For particle 1:

L1O=r1×p1L1O=r1×p1

And for particle 2:

L2O=r2×p2L2O=r2×p2

Since the particles are moving along parallel lines, their position vectors are parallel, and their magnitudes are equal, but their directions are opposite. Hence, r1=−r2r1=−r2.

Now, let's analyze the angular momentum of the system about point OO. The total angular momentum LtotalLtotal is the sum of the individual angular momenta:

Ltotal=L1O+L2OLtotal=L1O+L2O

Substituting the expressions for L1OL1O and L2OL2O, we get:

Ltotal=(r1×p1)+(r2×p2)Ltotal=(r1×p1)+(r2×p2)

Since r1=−r2r1=−r2, we can rewrite this as:

Ltotal=r1×(p1−p2)Ltotal=r1×(p1−p2)

Now, p1=mvp1=mv and p2=−mvp2=−mv (as the particles are moving in opposite directions), so:

p1−p2=mv−(−mv)=2mvp1−p2=mv−(−mv)=2mv

Substituting this back into the equation:

Ltotal=r1×(2mv)Ltotal=r1×(2mv)

Since r1r1 is the position vector of particle 1 relative to point OO, it doesn't change when we choose a different point. Therefore, LtotalLtotal remains the same regardless of the chosen point about which the angular momentum is calculated.

This demonstrates that the vector angular momentum of the two-particle system remains constant irrespective of the reference point chosen.