QBManager

Rotational Motion

269459 A circular disc of mass $4 kg$ and of radius $10 cm$ is rotating about its natural axis at the rate of $5 rad / \sec$ . its angular momentum is

1

0.25 {kgm}^{2} s^{- 1}

2

0.1 {kgm}^{2} s^{- 1}

3

2.5 {kgm}^{2} s^{- 1}

4

0.2 {kgm}^{2} s^{- 1}

Rotational Motion

269461 A child is standing with folded hands at thecentre of a platform rotating about its central axis. The K.E. of the system is K. The child now stretches his arms so that the M.I. of the system doubles. The K.E. of the system now is

1

2 K

2

K / 2

3

4 K

4

K / 4

Explanation:

$K E = \frac{L^{2}}{2 I}$

Rotational Motion

269462 If radius of earth shrinks by $0.1 %$ without change in its mass, the percentage change in the duration of one day

1 decrease by

0.1 %

2 increase by

0.1 %

3 decrease by

0.2 %

4 increase by

0.2 %

Explanation:

$I ω = \frac{2}{5} M R^{2} \times \frac{2 π}{T} ‖ =$ constant
$T \propto R^{2}$ and $\frac{Δ T}{T} = 2 \frac{Δ R}{R}$

Rotational Motion

269463 A ballet dancer spins about a vertical axis at 60rpm with his arms closed. Now he stretches his arms such that M.I. increases by $50 %$ . The new speed of revolution is

1

80 rpm

2

40 rpm

3

90 rpm

4

30 rpm

Explanation:

$I_{1} ω_{1} = I_{2} ω_{2}; I_{1} n_{1} = I_{2} n_{2}$

Rotational Motion

269464 A metallic circular wheel is rotating about its own axis without friction. If the radius of wheel expands by $0.2 %$ , percentage change in its angular velocity

1 increase by

0.1 %

2 decrease by

0.1 %

3 increase by

0.4 %

4 decrease by

0.4 %

Explanation:

$I ω = m r^{2} ω =$ constant
$ω \propto r^{- 2}$ and $\frac{Δ ω}{ω} = - 2 \frac{Δ r}{r}$

Rotational Motion

269459 A circular disc of mass $4 kg$ and of radius $10 cm$ is rotating about its natural axis at the rate of $5 rad / \sec$ . its angular momentum is

1

0.25 {kgm}^{2} s^{- 1}

2

0.1 {kgm}^{2} s^{- 1}

3

2.5 {kgm}^{2} s^{- 1}

4

0.2 {kgm}^{2} s^{- 1}

Rotational Motion

269461 A child is standing with folded hands at thecentre of a platform rotating about its central axis. The K.E. of the system is K. The child now stretches his arms so that the M.I. of the system doubles. The K.E. of the system now is

1

2 K

2

K / 2

3

4 K

4

K / 4

Explanation:

$K E = \frac{L^{2}}{2 I}$

Rotational Motion

269462 If radius of earth shrinks by $0.1 %$ without change in its mass, the percentage change in the duration of one day

1 decrease by

0.1 %

2 increase by

0.1 %

3 decrease by

0.2 %

4 increase by

0.2 %

Explanation:

$I ω = \frac{2}{5} M R^{2} \times \frac{2 π}{T} ‖ =$ constant
$T \propto R^{2}$ and $\frac{Δ T}{T} = 2 \frac{Δ R}{R}$

Rotational Motion

269463 A ballet dancer spins about a vertical axis at 60rpm with his arms closed. Now he stretches his arms such that M.I. increases by $50 %$ . The new speed of revolution is

1

80 rpm

2

40 rpm

3

90 rpm

4

30 rpm

Explanation:

$I_{1} ω_{1} = I_{2} ω_{2}; I_{1} n_{1} = I_{2} n_{2}$

Rotational Motion

269464 A metallic circular wheel is rotating about its own axis without friction. If the radius of wheel expands by $0.2 %$ , percentage change in its angular velocity

1 increase by

0.1 %

2 decrease by

0.1 %

3 increase by

0.4 %

4 decrease by

0.4 %

Explanation:

$I ω = m r^{2} ω =$ constant
$ω \propto r^{- 2}$ and $\frac{Δ ω}{ω} = - 2 \frac{Δ r}{r}$

Rotational Motion

269459 A circular disc of mass $4 kg$ and of radius $10 cm$ is rotating about its natural axis at the rate of $5 rad / \sec$ . its angular momentum is

1

0.25 {kgm}^{2} s^{- 1}

2

0.1 {kgm}^{2} s^{- 1}

3

2.5 {kgm}^{2} s^{- 1}

4

0.2 {kgm}^{2} s^{- 1}

Rotational Motion

269461 A child is standing with folded hands at thecentre of a platform rotating about its central axis. The K.E. of the system is K. The child now stretches his arms so that the M.I. of the system doubles. The K.E. of the system now is

1

2 K

2

K / 2

3

4 K

4

K / 4

Explanation:

$K E = \frac{L^{2}}{2 I}$

Rotational Motion

269462 If radius of earth shrinks by $0.1 %$ without change in its mass, the percentage change in the duration of one day

1 decrease by

0.1 %

2 increase by

0.1 %

3 decrease by

0.2 %

4 increase by

0.2 %

Explanation:

$I ω = \frac{2}{5} M R^{2} \times \frac{2 π}{T} ‖ =$ constant
$T \propto R^{2}$ and $\frac{Δ T}{T} = 2 \frac{Δ R}{R}$

Rotational Motion

269463 A ballet dancer spins about a vertical axis at 60rpm with his arms closed. Now he stretches his arms such that M.I. increases by $50 %$ . The new speed of revolution is

1

80 rpm

2

40 rpm

3

90 rpm

4

30 rpm

Explanation:

$I_{1} ω_{1} = I_{2} ω_{2}; I_{1} n_{1} = I_{2} n_{2}$

Rotational Motion

269464 A metallic circular wheel is rotating about its own axis without friction. If the radius of wheel expands by $0.2 %$ , percentage change in its angular velocity

1 increase by

0.1 %

2 decrease by

0.1 %

3 increase by

0.4 %

4 decrease by

0.4 %

Explanation:

$I ω = m r^{2} ω =$ constant
$ω \propto r^{- 2}$ and $\frac{Δ ω}{ω} = - 2 \frac{Δ r}{r}$

Rotational Motion

269459 A circular disc of mass $4 kg$ and of radius $10 cm$ is rotating about its natural axis at the rate of $5 rad / \sec$ . its angular momentum is

1

0.25 {kgm}^{2} s^{- 1}

2

0.1 {kgm}^{2} s^{- 1}

3

2.5 {kgm}^{2} s^{- 1}

4

0.2 {kgm}^{2} s^{- 1}

Rotational Motion

269461 A child is standing with folded hands at thecentre of a platform rotating about its central axis. The K.E. of the system is K. The child now stretches his arms so that the M.I. of the system doubles. The K.E. of the system now is

1

2 K

2

K / 2

3

4 K

4

K / 4

Explanation:

$K E = \frac{L^{2}}{2 I}$

Rotational Motion

269462 If radius of earth shrinks by $0.1 %$ without change in its mass, the percentage change in the duration of one day

1 decrease by

0.1 %

2 increase by

0.1 %

3 decrease by

0.2 %

4 increase by

0.2 %

Explanation:

$I ω = \frac{2}{5} M R^{2} \times \frac{2 π}{T} ‖ =$ constant
$T \propto R^{2}$ and $\frac{Δ T}{T} = 2 \frac{Δ R}{R}$

Rotational Motion

269463 A ballet dancer spins about a vertical axis at 60rpm with his arms closed. Now he stretches his arms such that M.I. increases by $50 %$ . The new speed of revolution is

1

80 rpm

2

40 rpm

3

90 rpm

4

30 rpm

Explanation:

$I_{1} ω_{1} = I_{2} ω_{2}; I_{1} n_{1} = I_{2} n_{2}$

Rotational Motion

269464 A metallic circular wheel is rotating about its own axis without friction. If the radius of wheel expands by $0.2 %$ , percentage change in its angular velocity

1 increase by

0.1 %

2 decrease by

0.1 %

3 increase by

0.4 %

4 decrease by

0.4 %

Explanation:

$I ω = m r^{2} ω =$ constant
$ω \propto r^{- 2}$ and $\frac{Δ ω}{ω} = - 2 \frac{Δ r}{r}$

Rotational Motion

269459 A circular disc of mass $4 kg$ and of radius $10 cm$ is rotating about its natural axis at the rate of $5 rad / \sec$ . its angular momentum is

1

0.25 {kgm}^{2} s^{- 1}

2

0.1 {kgm}^{2} s^{- 1}

3

2.5 {kgm}^{2} s^{- 1}

4

0.2 {kgm}^{2} s^{- 1}

Rotational Motion

269461 A child is standing with folded hands at thecentre of a platform rotating about its central axis. The K.E. of the system is K. The child now stretches his arms so that the M.I. of the system doubles. The K.E. of the system now is

1

2 K

2

K / 2

3

4 K

4

K / 4

Explanation:

$K E = \frac{L^{2}}{2 I}$

Rotational Motion

269462 If radius of earth shrinks by $0.1 %$ without change in its mass, the percentage change in the duration of one day

1 decrease by

0.1 %

2 increase by

0.1 %

3 decrease by

0.2 %

4 increase by

0.2 %

Explanation:

$I ω = \frac{2}{5} M R^{2} \times \frac{2 π}{T} ‖ =$ constant
$T \propto R^{2}$ and $\frac{Δ T}{T} = 2 \frac{Δ R}{R}$

Rotational Motion

269463 A ballet dancer spins about a vertical axis at 60rpm with his arms closed. Now he stretches his arms such that M.I. increases by $50 %$ . The new speed of revolution is

1

80 rpm

2

40 rpm

3

90 rpm

4

30 rpm

Explanation:

$I_{1} ω_{1} = I_{2} ω_{2}; I_{1} n_{1} = I_{2} n_{2}$

Rotational Motion

269464 A metallic circular wheel is rotating about its own axis without friction. If the radius of wheel expands by $0.2 %$ , percentage change in its angular velocity

1 increase by

0.1 %

2 decrease by

0.1 %

3 increase by

0.4 %

4 decrease by

0.4 %

Explanation:

$I ω = m r^{2} ω =$ constant
$ω \propto r^{- 2}$ and $\frac{Δ ω}{ω} = - 2 \frac{Δ r}{r}$