Solve-Work and Energy [PDF]

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3/97 The spring is unstretched when x=0. If the body moves from the initial position x1=100mm to the final position x2=200mm , (a) determine the work done by the spring on the body and (b) determine the work done on the body by its weight.



3/98 The small body has a speed vA=5 m/s at point A. Neglecting friction, determine its speed at point B after it has risen 0.8 m. Is knowledge of the shape of the track necessary?



3/99 The 64.4-lb crate slides down the curved path in the vertical plane. If the crate has a velocity of 3 ft/sec down the incline at A and a velocity of 25 ft/sec at B, compute the work done on the crate by friction during the motion from A to B.



3/100 The 1.5-lb collar slides with negligible friction on the fixed rod in the vertical plane. If the collar starts from rest at A under the action of the constant 2-lb horizontal force, calculate its velocity v as it hits the stop at B.



3/101 In the design of a spring bumper for a 3500-lb car, it is desired to bring the car to a stop from a speed of 5 mi/hr in a distance equal to 6 in. of spring deformation. Specify the required stiffness k for each of the two springs behind the bumper. The springs are undeformed at the start of impact.



3/102 A two-engine jet transport has a loaded weight of 90,000 lb and a forward thrust of 9800 lb per engine during takeoff. If the transport requires 4800 ft of level runway starting from rest to become airborne at a speed of 140 knots (1 knot= 1.151 mi/hr), determine the average resistance R to motion over the runway length due to drag (air resistance) and mechanical retardation by the landing gear. 3/103 The small collar of mass m is released from rest at A and slides down the curved rod in the vertical plane with negligible friction. Express the velocity v of the collar as it strikes the base at B in terms of the given conditions.



3/104 For the sliding collar of Prob. 3/103, if , m = 0.5 kg , b = 0.8 m and ,h=15 m and if the velocity of the collar as it strikes the base B is 4.70 m/s after release of the collar from rest at A, calculate the work Q of friction. What happens to the energy which is lost?