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# Engineering Mechanics - PKRB: Force and Animation

### Exercise

• General Questions
"I never see what has been done; I only see what remains to be done."
- Marie Curie
1.

The slender 200-kg beam is suspended by a cable at its end as shown. If a man pushes on its other end with a horizontal force of 30 N, determine the initial acceleration of its mass center G, the beam's angular acceleration, and the tension in the cable AB.

 A. aG = 0, = 0.225 rad/s2, T = 1.962 kN B. aG = 0.0750 m/s2, = 0.1125 rad/s2, T = 1.962 kN C. aG = 0, = 0.1125 rad/s2, T = 1.962 kN D. aG = 0.1500 m/s2, = 0.225 rad/s2, T = 1.962 kN

2.

A clown, mounted on stilts, loses his balance and falls backward from the position, where it is assumed the = 0 when = 07deg;. Paralyzed with fear, he remains rigid as he falls. His mass including the stilts is 80 kg, the mass center is at G, and the radius of gyration about G is kG = 1.2 m. Determine the coefficient of friction between his shoes and the ground at A if it is observed that slipping occurs when = 30°.

 A. = 0.833 B. = 0.468 C. = 0.243 D. = 0.400

3.

The dragster has a mass of 1.3 Mg and a center of mass at G. If a braking parachute is attached at C and provides a horizontal braking force FD, determine the maximum deceleration the dragster can have upon releasing the parachute without tipping the dragster over backwards (i.e., the normal force under the wheels and assume that the engine is disengaged so that the wheels are freely rolling.

 A. a = 16.35 m/s2 B. a = 8.46 m/s2 C. a = 2.75 m/s2 D. a = 35.0 m/s2

4.

The sports car has a mass of 1.5 Mg and a center of mass at G. Determine the shortest time it takes for it to reach a speed of 80 km/h, starting from rest, if the engine only drives the rear wheels, whereas the front wheels are free rolling. The coefficient of friction between the wheels and road is = 0.2. Neglect the mass of the wheels for the calculation.

 A. t = 17.49 s B. t = 18.12 s C. t = 18.76 s D. t = 22.7 s

5.

The disk has a mass of 20 kg and is originally spinning at the end of the massless strut with an angular velocity of = 60 rad/s. If it is then placed against the wall, for which A = 0.3, determine the time required for the motion to stop. What is the force in strut BC during this time?

 A. t = 3.11 s, FBC = 193.1 N B. t = 2.65 s, FBC = 227 N C. t = 5.30 s, FBC = 227 N D. t = 6.21 s, FBC = 193.1 N