The ground state energy of hydrogen atom is -13.6 eV. The kinetic energy of the electron
in this state is
27.2 eV
13.6 eV
6.8 eV
3.4 eV
A satellite is in a circular orbit round the earth at an altitude R above the earth's surface,where R is the radius of the earth. If g is the acceleration due to gravity on the surface of the earth the speed of the satellite is
The moment of inertia of a ring about one of its diameter is I. What will be its moment of inertia about a tangent parallel to the diameter?
I
2 I
I
3 I
A massless spring of natural length of 0.5 m and spring constant 50 N/m has one end fixed and the other end attached to mass of 250 g. The spring mass system is on a smooth floor. The mass is pulled until the length of the spring is 0.6 and then released from rest. The kinetic energy of the mass when the length of the spring is 0.5 m is
0.0176 J
2.25 J
6.25 J
9 J
A disc, initially at rest, starts rotating about its own axis, with a constant angular acceleration of 0.2 rad/s2. The time taken by the disc to rotate by 10 rad is (in second)
7.07
10
14.14
100
Two satellites S1 and S2 revolve round a planet in coplanar circular orbits in the same sense. Their periods of revolution are 1 h and 8 h respectively. The radius of the orbit of S1 is 104 km. The speed of S2 relative to S1 when they are closest, in km/h is
104
2 × 104
104
4 × 104
A.
104
From Kepler's law,
Velocity of first satellite
v1 =
=
Velocity of second satellite
v2 =
=
Velocity of S2 relative to
S1 = v2 − v1
=
=
∴ Relative speed =
A disc of a siren containing 60 holes rotates at a constant speed of 360 rpm. The emitted sound is in unison with a tuning fork of frequency
10 Hz
360 Hz
216 Hz
60 Hz
A particle performing uniform circular motion has angular momentum L. If its angular frequency is doubled and its kinetic energy halved, then the new angular momentum is
2L
4L
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 moments of inertia IX and IY is
IY = 321X
IY = 161X
IY = IX
IY = 641X
A 1 kg stone at the end of 1 m long string is whirled in a vertical circle at constant speed of 4 m/s. The tension in the string is 6 N, when the stone is a
top of the circle
bottom of the circle
halfway down
None of the above