The driver of a three-wheeler moving with a speed of 36 km/h sees a child
standing in the middle of the road and brings his vehicle to rest in 4.0 s just
in time to save the child. What is the average retarding force on the vehicle ?
The mass of the three-wheeler is 400 kg and the mass of the driver is 65 kg.
A body of mass 5 kg is acted upon by two perpendicular forces 8 N and 6 N.
Give the magnitude and direction of the acceleration of the body.
A constant force acting on a body of mass 3.0 kg changes its speed from 2.0 m s-1
to 3.5 m s-1 in 25 s. The direction of the motion of the body remains
unchanged. What is the magnitude and direction of the force ?
A constant retarding force of 50 N is applied to a body of mass 20 kg moving
initially with a speed of 15 m s-1. How long does the body take to stop ?
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].
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.
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.
An insect trapped in a
circular groove of radius 12 cm moves along
the groove steadily and completes 7
revolutions in 100 s. (a) What is the
angular speed, and the linear speed of the
motion? (b) Is the acceleration vector a
constant vector ? What is its magnitude ?
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