Two identical billiard balls
strike a rigid wall with the same speed but
at different angles, and get reflected without
any change in speed, as shown in Fig. 4.6.
What is (i) the direction of the force on the
wall due to each ball? (ii) the ratio of the
magnitudes of impulses imparted to the
balls by the wall ?
A batsman hits back a ball
straight in the direction of the bowler without
changing its initial speed of 12 m s–1
.
If the mass of the ball is 0.15 kg, determine
the impulse imparted to the ball. (Assume
linear motion of the ball)
The motion of a particle of
mass m is described by y = +
1 2
2
ut gt . Find
the force acting on the particle.
A bullet of mass 0.04 kg
moving with a speed of 90 m s–1 enters a
heavy wooden block and is stopped after a
distance of 60 cm. What is the average
resistive force exerted by the block on the
bullet?
An astronaut accidentally
gets separated out of his small spaceship
accelerating in inter stellar space at a
constant rate of 100 m s–2. What is the
acceleration of the astronaut the instant after
he is outside the spaceship ? (Assume that
there are no nearby stars to exert
gravitational force on him.)
If, in Exercise 4.21, the speed of the stone is increased beyond the maximum permissible
value, and the string breaks suddenly, which of the following correctly describes the
trajectory of the stone after the string breaks :
(a) the stone moves radially outwards,
(b) the stone flies off tangentially from the instant the string breaks,
(c) the stone flies off at an angle with the tangent whose magnitude depends on the
speed of the particle ?
Explain why
(a) a horse cannot pull a cart and run in empty space,
(b) passengers are thrown forward from their seats when a speeding bus stops
suddenly,
(c) it is easier to pull a lawn mower than to push it,
(d) a cricketer moves his hands backwards while holding a catch.
A stone of mass 0.25 kg tied to the end of a string is whirled round in a circle of radius
1.5 m with a speed of 40 rev./min in a horizontal plane. What is the tension in the
string ? What is the maximum speed with which the stone can be whirled around if
the string can withstand a maximum tension of 200 N ?
A batsman deflects a ball by an angle of 45° without changing its initial speed which is
equal to 54 km/h. What is the impulse imparted to the ball ? (Mass of the ball is 0.15 kg.)
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