Engineering Mechanics

(^620) „„„„„ A Textbook of Engineering Mechanics
EXERCISE 30.3

1. A truck of mass 1.5 t is running at a speed of 54 km.p.h. Find its kinetic energy. If the
   resistance to the motion is 100 newtons, find how far the truck will run before it stops.
   (Ans. 168.75 kJ ; 1125 m)


2. A bullet moving at the rate of 300 m/s is fired into a thick target and penetrates up to 500
   mm. If it is fired into a 250 mm thick target, find the velocity of emergence. Take resis-
   tance to be uniform in both cases. (Ans. 212.1 m/s)


3. A body of mass 2 kg is thrown vertically upwards with an initial velocity of 9.8 m/s. Find
   its kinetic energy (i) at the moment of its propulsion ; (ii) after half a second ; and (iii) after
   one second. (Ans. 96.04 N-m ; 2401 N-m ; 0)


4. A railway wagon of mass 20 tonnes runs into a buffer stop having two buffer springs each
   of 10 kN/mm stiffness. Find the maximum compression of the springs, if the wagon is
   travelling at 18 km.p.h. (Ans. 158 mm)


5. A block of mass 5 kg is released from rest on an inclined plane as shown in Fig. 30.13.

Fig. 30.13

Find the maximum compression of the spring, if the spring constant is 1 N/mm and the

coefficient of friction between the block and the inclined plane is 0.2. (Ans. 160 mm)

6. A hammer of mass 400 kg falls through a height of 3 m on a pile of negligible mass. If it
   drives the pile 1 m into the ground, find the average resistance of the ground for penetration.
   (Ans. 15.7 kN)


7. A pile hammer of mass 1500 kg drops from a height of 600 mm on a pile of mass 750 kg.
   The pile penetrates 50 mm per blow. Assuming that the motion of the pile is resisted by a
   constant force, find the resistance to penetration of the ground. (Ans. 139.7 kN)

QUESTIONS

1. Explain the term ‘work’. When the work is said to be done?


2. What are the units of work done? What is the relation between work done and power?


3. What do you understand by the term ‘energy’? Explain the various forms of mechanical
   energies.


4. Explain the term ‘conservation of energy’.

OBJECTIVE TYPE QUESTIONS

1. The unit of work done in S.I. system is
   (a) Newton (b) Joule (c) Watt


2. The work done is said to be zero, when
   (a) some force acts on a body, but displacement is zero.