## The angular acceleration of a fly wheel is given by α = 12 – t, where α is in rad s-2 and t in second….

Q: The angular acceleration of a fly wheel is given by α = 12 – t, where α is in rad s-2 and t in second. If the angular velocity of the wheel is 60 rad s-1 at the end of 4 s, the angular velocity at the end of 6 s and the number of revolutions that take place in these 6 s, respectively are

(a) 54 rads-1, 37.8

(b) 84 rads-1, 57.8

(c) 74 rads-1, 47.8

(d) 80 rads-1, 50

Ans: (c)

## A wheel of moment of inertia I and radius R is rotating about its axis at an angular speed ωo….

Q: A wheel of moment of inertia I and radius R is rotating about its axis at an angular speed ω0. It picks up a stationary particle of mass m at its edge. Find the new angular speed of the wheel.

(a) $\displaystyle \frac{2 I \omega_0}{I + MR^2}$

(b) $\displaystyle \frac{ I \omega_0}{I + MR^2}$

(c) $\displaystyle \frac{ I \omega_0}{I + 2 MR^2}$

(d) $\displaystyle \frac{ I \omega_0}{2 I + MR^2}$

Ans: (b)

## A circular disc X of radius R is made from an iron plate of thickness t and another disc Y of radius 4R is…

Q: A circular disc X of radius R is made from an iron plate of thickness t and another disc Y of radius 4R is made from an iron plate of thickness t/4. Then, the relation between the moment of inertia IX and IY is

(a) IY = 32 IX

(b) IY = 16 IX

(c) IY = IX

(d) IY = 64 IX

Ans: (d)

## A square plate of mass 120g and edge 5.0 cm rotates about one of the edges. If it has …

Q:A square plate of mass 120g and edge 5.0 cm rotates about one of the edges. If it has a uniform angular acceleration of 0.2 rad/s², The torque acting on the plate is

(a) 3 × 10-5 N-m

(b) 2 × 10-5 N-m

(c) 3 × 10-4 N-m

(d) 3 × 10-4 N-m

Ans: (a)

## A simple pendulum of length l is pulled aside to make an angle θ with the vertical. …

Q: A simple pendulum of length l is pulled aside to make an angle θ with the vertical. The magnitude of the torque of the weight w of the bob about the point of suspension is

(a) w l

(b) wl sinθ

(c) wl tanθ

(d) w l cosθ

Ans: (b)