One end of a string of length l is connected to a particle of mass m and the
other to a small peg on a smooth horizontal table. If the particle moves in a
circle with speed v the net force on the particle (directed towards the centre)
is :
(i) T, (ii) l
mv T
2
− , (iii) l
mv +T
2
, (iv) 0
T is the tension in the string. [Choose the correct alternative].
State two economically important uses of:
(a) heterotrophic bacteria
(b) archaebacteria
Give the magnitude and direction of the net force acting on a stone of mass
0.1 kg,
(a) just after it is dropped from the window of a stationary train,
(b) just after it is dropped from the window of a train running at a constant
velocity of 36 km/h,
(c ) just after it is dropped from the window of a train accelerating with 1 m s-2
,
(d) lying on the floor of a train which is accelerating with 1 m s-2, the stone
being at rest relative to the train.
Neglect air resistance throughout.
Discuss how classification systems have undergone several changes over a
period of time?
Give the magnitude and direction of the net force acting on
(a) a drop of rain falling down with a constant speed,
(b) a cork of mass 10 g floating on water,
(c) a kite skillfully held stationary in the sky,
(d) a car moving with a constant velocity of 30 km/h on a rough road,
(e) a high-speed electron in space far from all material objects, and free of
electric and magnetic fields.
A pebble of mass 0.05 kg is thrown vertically upwards. Give the direction
and magnitude of the net force on the pebble,
(a) during its upward motion,
(b) during its downward motion,
(c) at the highest point where it is momentarily at rest. Do your answers
change if the pebble was thrown at an angle of 45° with the horizontal
direction?
Ignore air resistance.
Illustrate the taxonomical hierarchy with suitable examples of a plant
and an animal.
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