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# Engineering Mechanics - KOP: Impulse and Momentum

### Exercise

• General Questions
"You cannot shake hands with a clenched fist."
- Indira Gandhi
16.

A girl having a weight of 40 lb slides down the smooth slide onto the surface of a 20-lb wagon. Determine the speed of the wagon at the instant the girl stops sliding on it. If someone ties the wagon to the slide at B, determine the horizontal impulse the girl will exert at C in order to stop her motion. Neglect friction and assume that the girl starts from rest at the top of the slide, A.

 A. vwagon = 20.7 ft/s Imp = 38.6 lb-s B. vwagon = 31.1 ft/s Imp = 38.6 lb-s C. vwagon = 31.1 ft/s Imp = 57.9 lb-s D. vwagon = 20.7 ft/s Imp = 57.9 lb-s

17.

A hockey puck is traveling to the left with a velocity of v1 = 10 m/s when it is struck by a hockey stick and given a velocity of v2 = 20 m/s as shown. Determine the magnitude of the net impulse exerted by the hockey stick on the puck. The puck has a mass of 0.2 kg.

 A. Imp = 6.00 N-s B. Imp = 2.00 N-s C. Imp = 2.78 N-s D. Imp = 5.68 N-s

18.

A rifle has a mass of 2.5 kg. If it is loosely gripped and a 1.5-g bullet is fired from it with a muzzle velocity of 1400 m/s, determine the recoil velocity of the rifle just after firing.

 A. vrifle = 0.840 m/s B. vrifle = 0.525 m/s C. vrifle = 2.33 m/s D. vrifle = 1.400 m/s

19.

The two blocks A and B each have a mass of 500 g. The blocks are fixed to the horizontal rods and their initial velocity is 2 m/s in the direction shown. If a couple moment of M = 0.8 N • m is applied about CD of the frame, determine the speed of the block in 4 s. The mass of the supporting frame is negligible and its free to rotate about CD.

 A. v2 = 10.67 m/s B. v2 = 23.3 m/s C. v2 = 22.3 m/s D. v2 = 12.67 m/s

20.

A boy, having a weight of 90 lb, jumps off a wagon with a relative velocity of vb/w = 6 ft/s. If the angle of jump is 30°, determine the horizontal velocity (vw)2 of the wagon just after the jump. Originally both the wagon and the boy are at rest. Also, compute the total average impulsive force that all four wheels of the wagon exert on the ground of the boy jumps off in t = 0.8s. The wagon has a weight of 20 lb.

 A. vwagon = 23.4 ft/s Nwheel = 110.0 lb B. vwagon = 23.4 ft/s Nwheel = 120.5 lb C. vwagon = 4.25 ft/s Nwheel = 120.5 lb D. vwagon = 4.25 ft/s Nwheel = 110.0 lb