Campbell Biology

Work and Energy.
1. What is the work done by a force of 20 N acting through a parallel distance of 8.0 m?
What force will do the same work through a distance of 4.0 m? [160 J, 40 N]
2. A push of 120 N is applied along the handle of a lawn mower producing a horizontal displacement of 14.0 m. If the handle makes an angle of 30.0o with the ground, what work was done by the 120 N force? [1.45×103 J]
3. A rope making an angle of 35.0o drags a 10.0 kg toolbox a horizontal distance of 20.0
m. The tension in the rope is 60.0 N and the constant friction force is 30.0 N. What work is done by the rope? What work is done by friction? What is the resultant work?
What is the coefficient of friction between the toolbox and the floor? [983 J, -600 J,
383 J, 0.472]
4. A box of mass 5.0 kg is accelerated by a force across a floor at a rate of 2.0 m/s2 for
7.0 s. Find the net work done on the box. [490 J]
5. A 200 g mass wooden block was placed on an inclined plane and the angle of the incline was slowly increased until the block begins to slide.
(a) If the coefficient of static friction is 0.30, what is the angle at which it begins to slide? [16.7o
]
(b) The wooden block is then allowed to slide down the incline. If the length of the incline was 1.0 m, find the work done by the frictional force as it slides down, given that coefficient of kinetic friction is 0.20. [-0.375 J]
(c) Using energy considerations, find the final velocity at the bottom of the incline if it slides down from rest. [1.37 m/s]
6. What is the minimum work needed to push a 950-kg car 810 m up along a 9.0º incline? (a) Ignore friction. (b) Assume the effective coefficient of friction retarding the car is 0.25. [(a) 1.2×106 J, (b) 3.0×106 J]
7. A spring has k = 88 N/m. Use a graph to determine the work needed to stretch it from x = 3.8 cm to x = 5.8 cm where x is the displacement from its un-stretched length.
[8.4×10-2 J]
8. The net force exerted on a particle acts in the +x direction. Its magnitude increases linearly from zero at x = 0 to 24.0 N at x = 3.0 m. It remains constant at 24.0 N from x = 3.0 m to x = 8.0 m and then decreases linearly to zero at x = 13.0 m. Determine the work done to move the particle from x = 0 to x = 13.0 m graphically by determining the area under the Fx vs x graph. [216 J]