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Mass and Gravitational Potential Energy

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WORK and ENERGY

Work done by a constant force
1- The drawing shows a plane diving toward the ground and then climbing back upward. During each of these motions, the lift force acts perpendicular to the displacement , which has the same magnitude, 1.7 × 103 m, in each case. The engines of the plane exert a thrust , which points in the direction of the displacement and has the same magnitude during the dive and the climb. The weight of the plane has a magnitude of 5.9 × 104 N. In both motions, net work is performed due to the combined action of the forces , and .

a. Is more net work done during the dive or the climb? Explain.
b. Find the difference between the net work done during the dive and the climb.…show more content…
The coefficient of kinetic friction, µk , between the bike tires and the road.

13- The figure below depicts the motion of a mass m = 300 kg as it slides along a track, which has one smooth segment and two rough segments of kinetic friction coefficient of 0.4. If the mass was released from rest at point A on the track,

a. Find the point where the KE of the mass is zero (i.e. point E where the mass comes to a complete stop)
b. Plot (draw) the kinetic energy of the 300 kg mass as a function of position from point A until point D. [Show all work, use proper scale, show equations and substitution with units and show all points on the graph].

14- The ambulance shown in the figure below (3000 kg) slides down a frictionless incline that is 10m long. It starts from rest at point A. Then it continues along a rough surface (BC) until it comes to a complete stop at point C.

a. Calculate its speed at point B
b. If the coefficient of kinetic friction of the rough segment (BC) is 0.1, calculate the distance d the ambulance slides on before stopping.

Power
15- Bicyclists in the Tour de France do enormous amounts of work during a race. For example, the average power per kilogram generated by Lance Armstrong (m = 75.0 kg) is 6.50 W per kilogram of his body mass.
a. How much work does he do during a 135-km race in which his average speed is 12.0 m/s?
b. Often, the work done is expressed in nutritional Calories rather than in joules. Express the
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