Dynamics Chapter 15

Jet engines on the 100 Mg VTOL aircraft exert a constant vertical force of 981 kN as it hovers. Determine the net impulse on the aircraft over t = 10 s. A) -981 kN·s B) 0 kN·s C) 981 kN·s D) 9810 kN·s

0 kN·s Since V1 = V2 = 0, there is no net impulse

Calculate the impulse due to the force. A) 20 kg·m/s B) 10 kg·m/s C) 5 N·s D) 15 N·s

10 kg·m/s Area under curve = 2(.5)(1 s)(10 N) = 10 N•s = 10 (kg)(m/s2)(s) = 10 kg•m/s

A 100 lb cabinet is placed on a smooth surface. If a force of a 100 lb is applied for 2 s, determine the net impulse on the cabinet during this time interval. A) 0 lb·s B) 100 lb·s C) 200 lb·s D) 300 lb·s

100 lb·s 100(2 ) -100sin(30º) (2) = 100 lb•s

Over the short time span of a tennis ball hitting the racket during a player's serve, the ball's weight can be considered _____________ A) nonimpulsive. B) impulsive. C) not subject to Newton's second law. D) Both A and C.

A) nonimpulsive.

If a particle moves in the z - y plane, its angular momentum vector is in the A) x direction. B) y direction. C) z direction. D) z - y direction.

A) x direction

Which parameter is not involved in the linear impulse and momentum equation? A) Velocity B) Displacement C) Time D) Force

B) Displacement

The 200-g baseball has a horizontal velocity of 30 m/s when it is struck by the bat, B, weighing 900-g, moving at 47 m/s. During the impact with the bat, how many impulses of importance are used to find the final velocity of the ball? A) Zero B) One C) Two D) Three

B) One

A particle strikes the smooth surface with a velocity of 30 m/s. If e = 0.8, (vx) 2 is _____ after the collision. A) zero B) equal to (vx) 1 C) less than (vx) 1 D) greater than (vx) 1

B) equal to (vx) 1

The linear impulse and momentum equation is obtained by integrating the ______ with respect to time. A) friction force B) equation of motion C) kinetic energy D) potential energy

B) equation of motion

When the motion of one or both of the particles is at an angle to the line of impact, the impact is said to be ________ A) central impact. B) oblique impact. C) major impact. D) None of the above.

B) oblique impact.

Select the correct expression for the angular momentum of a particle about a point. A) r × v B) r × (m v) C) v × r D) (m v) × r

B) r × (m v)

The ratio of the restitution impulse to the deformation impulse is called _________ A) impulse ratio. B) restitution coefficient. C) energy ratio. D) mechanical efficiency.

B) restitution coefficient.

The internal impulses acting on a system of particles always __________ A) equal the external impulses B) sum to zero. C) equal the impulse of weight. D) None of the above.

B) sum to zero.

A constant force F is applied for 2 s to change the particle's velocity from v1 to v2. Determine the force F if the particle's mass is 2 kg. A) (17.3 j) N B) (-10 i +17.3 j) N C) (20 i +17.3 j) N D) ( 10 i +17.3 j) N

C) (20 i +17.3 j) N D F∆T=m∆v → 2F = 2[(10i+17.3j) - (-10i) ] = (20i + 17.3j) N

If an impulse-momentum analysis is considered during the very short time of interaction, as shown in the picture, weight is a/an __________ A) impulsive force. B) explosive force. C) non-impulsive force. D) internal force

C) non-impulsive force. It is non-impulsive since the weight will have a negligible effect on the change in momentum

The sum of the moments of all external forces acting on a particle is equal to A) angular momentum of the particle. B) linear momentum of the particle. C) time rate of change of angular momentum. D) time rate of change of linear momentum.

C) time rate of change of angular momentum

If a particle moves in the x - y plane, its angular momentum vector is in the A) x direction. B) y direction. C) z direction. D) x - y direction.

C) z direction

Block B (1 kg) is moving on the smooth surface at 10 m/s when it squarely strikes block A (3 kg), which is at rest. If the velocity of block A after the collision is 4 m/s to the right, (vB)2 is A) 2 m/s → B) 7 m/s ← C) 7 m/s → D) 2 m/s ←

D) 2 m/s ← (1)(10) + 0 = (1)(VB)2 + (3)(4). Thus, (VB)2 = 2 m/s

The 20 g bullet is fired horizontally at 1200 m/s into the 300 g block resting on a smooth surface. If the bullet becomes embedded in the block, what is the velocity of the block immediately after impact. A) 1125 m/s B) 80 m/s C) 1200 m/s D) 75 m/s

D) 75 m/s

A ball is traveling on a smooth surface in a 3 ft radius circle with a speed of 6 ft/s. If the attached cord is pulled down with a constant speed of 2 ft/s, which of the following principles can be applied to solve for the velocity of the ball when r = 2 ft? A) Conservation of energy B) Conservation of linear momentum C) Conservation of mass D) None of the above

D) None of the above

If there are no external impulses acting on a particle A) only linear momentum is conserved. B) only angular momentum is conserved. C) both linear momentum and angular momentum are conserved. D) neither linear momentum nor angular momentum are conserved.

both linear momentum and angular momentum are conserved.

Under what condition is the energy lost during a collision maximum? A) e = 1.0 B) e = 0.0 C) e = -1.0 D) Collision is non-elastic.

e=0.0

A drill rod is used with a air hammer for making holes in hard rock so explosives can be placed in them. How many impulsive forces act on the drill rod during the drilling? A) None B) One C) Two D) Three

two The impact on the top of the rod is one impulsive force and the impact of the hard rock on the rod is the other. This assumes the weight of the rod itself is small in comparison to the other two forces

Two balls impact with a coefficient of restitution of 0.79. Can one of the balls leave the impact with a kinetic energy greater than before the impact? A) Yes B) No C) Impossible to tell D) Don't pick this one!

yes