Mechanical Engineering Principles

LINEAR MOMENTUM AND IMPULSE 143

Exercise 61 Short answer questions on lin-
ear momentum and impulse

1. Define momentum.


2. State Newton’s first law of motion.


3. State the principle of the conservation of
   momentum.


4. State Newton’s second law of motion.


5. Define impulse.


6. What is meant by an impulsive force?


7. State Newton’s third law of motion.

Exercise 62 Multi-choice questions on lin-
ear momentum and impulse
(Answers on page 284)

1. A mass of 100 g has a momentum of
   100 kg m/s. The velocity of the mass is:

(a) 10 m/s (b) 10^2 m/s

(c) 10−^3 m/s (d) 10^3 m/s

2. A rifle bullet has a mass of 50 g. The
   momentum when the muzzle velocity is
   108 km/h is:

(a)54kgm/s (b)1.5kgm/s

(c) 15000 kg m/s (d) 21.6 kg m/s

A bodyPof mass 10 kg has a velocity

of 5 m/s and the same line of action as

a bodyQof mass 2 kg and having a

velocity of 25 m/s. The bodies collide,

and their velocities are the same after

impact. In questions 3 to 6, select the

correct answer from the following:

(a) 25/3 m/s (b) 360 kg m/s (c) 0

(d) 30 m/s (e) 160 kg m/s

(f) 100 kg m/s (g) 20 m/s

3. Determine the total momentum of the
   system before impact when P andQ
   have the same sense.
   4. Determine the total momentum of the
   system before impact when P andQ
   have the opposite sense.
   5. Determine the velocity ofPandQafter
   impact if their sense is the same before
   impact.
   6. Determine the velocity ofPandQafter
   impact if their sense is opposite before
   impact.
   7. A force of 100 N acts on a body of mass
   10 kg for 0.1 s. The change in velocity
   of the body is:

(a) 1 m/s (b) 100 m/s

(c) 0.1 m/s (d) 0.01 m/s

A vertical pile of mass 200 kg is driven

100 mm into the ground by the blow of a

1 t hammer which falls through 1.25 m.

In questions 8 to 12, takegas 10 m/s^2

and select the correct answer from the

following:

(a) 25 m/s (b) 25/6 m/s

(c) 5 kg m/s (d) 0

(e) 625/6 kN (f) 5000 kg m/s

(g) 5 m/s (h) 12 kN

8. Calculate the velocity of the hammer
   immediately before impact.


9. Calculate the momentum of the hammer
   just before impact.


10. Calculate the momentum of the ham-
    mer and pile immediately after impact
    assuming they have the same velo-
    city.


11. Calculate the velocity of the hammer and
    pile immediately after impact assuming
    they have the same velocity.


12. Calculate the resistive force of the
    ground, assuming it to be uniform.