9. A worker pushing a 35.0-kg wooden crate at a constant AMT speed for 12.0 m al
ID: 1395219 • Letter: 9
Question
9. A worker pushing a 35.0-kg wooden crate at a constant AMT speed for 12.0 m along a wood floor does 350 J of work by applying a constant horizontal force of magnitude F on the crate. (a) Determine the value of F. (b) Ifthe worker now applies a force greater than F, describe the subsequent motion of the crate. (c) Describe what would happen to the crate if the applied force is less than F. 10. A7.80-g bullet moving at 575 m/s strikes the hand of a superhero, causing the hand to move 5.50 cm in the direction of the bullet's velocity before stopping. (a) Use work and energy considerations to find the average force that stops the bullet. (b) Assuming the force is constant, determine how much time elapses between the moment the bullet strikes the hand and the moment it stops moving 11. The potential energy of a system of two particles separated by a distance r is given by U(r) A/r, where A is a constant. Find the radial force Fr that each particle exerts on the other. 12. A baseball outfielder throws a 0.150-kg base-ball at a speed of 40.0 m/s and an initial angle of 30.0° to the horizontal. What is the kinetic energy of the baseball at the highest point of its trajectory? 13. An 820-N Marine in basic training climbs a 12.0-m W vertical rope at a constant speed in 8.00 s. What is his power output? 14. A block of mass 0.250 kg is placed on top of a light, vertical spring of force constant 5 000 N/m and pushed downward so that the spring is compressed by 0.100 m. After the block is released from rest, it travels upward and then leaves the spring. To what maximum height above the point of release does it rise? 15. An older-model car accelerates from 0 to speed vin a time interval of At. A newer, more powerful sports car accelerates from 0 to 2v in the same time period. Assuming the energy coming from the engine appears only as kinetic energy of the cars, compare the power of the two cars.Explanation / Answer
9) a) F = W / d
= 350 / 12
= 29.17 N
b) The force F = 29.17 N computed above was moving the grate at constant speed (Balancing friction), any increase above 29.17 N will just accelerate the grate which will move with increasing speed.
c) If the applied force is less , friction will ocercome the applied force which will decelerate the grate and slow it down till finally rest
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