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0593_C09_fm Page 311 Monday, May 6, 2002 2:50 PM

Principles of Impulse and Momentum 311

conserved or unchanged. The analyst then need only be concerned with velocities, thus
avoiding the calculation of accelerations and the evaluation of force systems as required
with Newton’s law and d’Alembert’s principle. In the next chapter we will consider energy
methods that also avoid the calculation of accelerations.

Problems

Section 9.2 Impulse
P9.2.1: A triangular impulsive force F has a profile with magnitude as in Figure P9.2.1. If
F is in the direction of a unit vector n, determine the resulting impulse I.

5000 lb

Force

FIGURE P9.2.1
Impulsive force magnitude. O 0.1 Time (sec)

P9.2.2: A 3000-lb automobile collides with a fixed barrier producing a deceleration of the
car as in Figure P9.2.2. Determine the magnitude of the impulse.

Deceleration
28 g

FIGURE P9.2.2
0.02 0.1 Time (sec)
Deceleration profile.
P9.2.3: A brake for a rotor creates a moment about the axis of the rotor (or parallel to the
axis of the rotor) with the magnitude of the moment depicted in Figure P9.2.3. Let n be
a unit vector parallel to the axis of the rotor and in the direction of rotation of the rotor
(according to the right-hand rule). Determine the angular impulse J of the braking moment.

Section 9.3 Linear Momentums

P9.3.1: A 15-lb particle P has a velocity 6n – 3n + 8n ft/sec, where n , n , and n are
3
3
2
1
1
2
mutually perpendicular unit vectors. Find the linear momentum of P. Express the result
in both English and international (SI) units.