BoardPhysics

Center of Mass and System of Particles

5 Board Physics previous year questions on Center of Mass and System of Particles — options free on every question; 1 include the answer & explanation free, the rest unlock with PYQ Pass.

Q1 FREE PREVIEW
PYQ

A disc of radius 20 cm has its center at origin. If a disc of radius 5 cm is cut from it such that its edge touches the edge of the bigger disc, find the location of centre of mass of the new system.

(Shift I Memory Based)

a

(-1 cm, 0 cm)

b

(-1 cm, -1 cm)

c

(1 cm, 1 cm)

d

(1cm, - 1 cm)

✓ Correct answer: a)

(-1 cm, 0 cm)

Explanation

R = 20 cm, r = 5 cm

Let the mass of big disc is M and the small disc is m.

\(\mathrm{Mass}\mathrm{per}\mathrm{unit}\mathrm{area}=\frac{\mathrm{M}}{\pi {\left(20\right)}^{2}}\\ \mathrm{mass}\mathrm{of}\mathrm{smaller}\mathrm{disc},\mathrm{m}=\frac{\mathrm{M}}{\pi {\left(20\right)}^{2}}\times \pi {\left(5\right)}^{2}=\frac{\mathrm{M}}{16}\)

The coordinates of centre of mass is given as

\({\mathrm{x}}_{\mathrm{cm}}=\frac{\mathrm{M}\times 0-\mathrm{m}\times 15}{\mathrm{M}-\mathrm{m}}=\frac{-\frac{\mathrm{M}}{16}\times 15}{\mathrm{M}-\frac{\mathrm{M}}{16}}=-1\mathrm{cm}\\ {\mathrm{y}}_{\mathrm{cm}}=0\mathrm{cm}\)

Q2
PYQ

A disc of radius 20 cm has its center at origin. If a disc of radius 5 cm is cut from it such that its edge touches the edge of the bigger disc, find the location of centre of mass of the new system.

(Shift I Memory Based)

a

(-1 cm, 0 cm)

b

(-1 cm, -1 cm)

c

(1 cm, 1 cm)

d

(1cm, - 1 cm)

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Q3
PYQ

Consider a circular disc of radius 20 cm with centre located at the origin. A circular hole of radius 5 cm is cut from this disc in such a way that the edge of the hole touches the edge of the disc. The distance of centre of mass of residual or remaining disc from the origin will be

[JEE Main 2025, 23 Jan (Shift 1)]

a

0.5 cm

b

2.0 cm

c

1 .5 cm

d

1 .0 cm

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Q4
PYQ

Two bodies A and B of same mass undergo completely inelastic one dimensional collision. The body A moves with velocity \({v}_{1}\) while body B is at rest before collision. The velocity of the system after collision is \({v}_{2}\). The ratio \({v}_{1}:{v}_{2}\) is :

[NEET 2024]

a

1 : 2

b

2 : 1

c

4 : 1

d

1 : 4

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Q5
PYQ

Two bodies A and B of same mass undergo completely inelastic one dimensional collision. The body A moves with velocity \({v}_{1}\) while body B is at rest before collision. The velocity of the system after collision is \({v}_{2}\). The ratio \({v}_{1}:{v}_{2}\) is :

a

1 : 2

b

2 : 1

c

4 : 1

d

1 : 4

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