Download App

Rotational Mechanics — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsRotational Mechanics3 Marks
Question
A body rotating at 20rad/s is acted upon by a constant torque providing it a deceleration of $2rad/s^2.$ At what time will the body have kinetic energy same as the initial value if the torque continues to act?
✓

Answer

Initial angular velocity = 20rad/s Therefore $\alpha=2\text{rad/s}^2$
$\Rightarrow\text{t}_1=\frac{\omega_2}{\alpha_1}=\frac{20}{2}=10\text{sec}$
Therefore 10sec it will come to rest. Since the same torque is continues to act on the body it will produce same angular acceleration and since the initial kinetic energy = the kinetic energy at a instant. So initial angular velocity = angular velocity at that instant Therefore time require to come to that angular velocity,
$\Rightarrow\text{t}_2=\frac{\omega}{\alpha_2}=\frac{20}{2}=10\text{sec}$
therefore time required $= t_1 + t_2 = 20$sec.

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "3 Marks Question" from Rotational Mechanics→Rotational Mechanics — all question types→Physics STD 12 Science question papers→Gujarat Board STD 12 Science question papers→Gujarat Board question paper generator→

Similar questions

Given n resistors each of resistance R, how will you combine them to get the (i) maximum (ii) minimum effective resistance? What is the ratio of the maximum to minimum resistance?
→
Find the ratio of the lengths of an iron rod and an aluminium rod for which the difference in the lengths is independent of temperature. Coefficients of linear expansion of iron and aluminium are ${12 \times 10^{-6}}  ^\circ C^{-1}$ and ${23 \times 10^{-6}}^\circ C^{-1}$ respectively.
→
A cyclotron’s oscillator frequency is 10MHz. What should be the operating magnetic field for accelerating protons? If the radius of its ‘dees’ is 60 cm, calculate the kinetic energy (in MeV) of the proton beam produced by the accelerator.
→
  1. State Bohr’s postulate to define stable orbits in hydrogen atom. How does de Broglie’s hypothesis explain the stability of these orbits?
  2. A hydrogen atom initially in the ground state absorbs a photon which excites it to the n = 4 level. Estimate the frequency of the photon.
→
Explain, with the help of a schematic diagram, the principle and working of a Light Emitting Diode. What criterion is kept in mind while choosing the semiconductor material for such a device? Write any two advantages of Light Emitting Diode over conventional incandescent lamps.
→
  1. How are electromagnetic waves produced? Explain.
  2. A plane electromagnetic wave is travelling through a medium along the +ve z-direction. Depict the electromagnetic wave showing the directions of the oscillating electric and magnetic fields.
→
Two heated wires of the same dimensions are first connected in series and then in parallel to a source of supply. What will be the ratio of heat produced in the two cases?
→
Define electric current and current density. By giving an example prove that electric current is a scalar quantity but not a vector quantity. Explain electric current in any conductor.
→
A plate of area $10cm^2$​​​​​​​ is to be electroplated with copper (density $9000kg/m^3$) to a thickness of 10 micrometres on both sides, using a cell of 12V. Calculate the energy spent by the cell in the process of deposition. If this energy is used to heat 100g of water, calculate the rise in the temperature of the water. ECE of copper $= 3 \times 10^{-7}kg C^{-1}$ and specific heat capacity of water $= 4200Jkg^{-1}.$
→
What is the de Broglie wavelength associated with $(a)$ an electron moving with a speed of $5.4 \times 10^6 m / s$, and $(b)$ a ball of mass $150 g$ travelling at $30.0 m / s$ ?
→