ASSIGNMENT 5 Keys

ASSIGNMENT 5 keys

1. Knight 5.007. [454965] Show Details Figure Ex5.7 shows the velocity graph of a 5.0 kg object as it moves along the x- axis. What is the net force acting on this object at the given times?

Figure Ex5.7 t = 3 s [20] N t = 5 s [0] N t = 7 s [-30] N

2. Knight 5.009. [370365] Show Details A horizontal rope is tied to a 46 kg box on frictionless ice. What is the tension in the rope under each of the following conditions? (a) the box is at rest [0] N (b) the box moves at a steady 5.0 m/s [0] N 2 (c) the box has vx = 5.0 m/s and ax = 5.0 m/s [230] N

3. Knight 5.006. [484209] Show Details In each of the two free-body diagrams, the forces are acting on a 2.2 kg object. For each diagram, find the values of ax and ay, the x- and y-components of the acceleration, with F1 = 5 N and F2 = 4 N. (a) Diagram A ax = [1.35] m/s2 ay = [0] m/s2 (b) Diagram B ax = [-0.705] m/s2 ay = [0] m/s2

4. Knight 5.001. [484202] Show Details The three ropes in the figure are tied to a small, very light ring. Two of the ropes are anchored to walls at right angles, and the third rope pulls as shown, with T3 = 98 N and = 32°. What are T1 and T2, the magnitudes of the tension forces in the first two ropes?

T1 = [83.1] N

T2 = [51.9] N

5. Knight 5.002. [454971] Show Details The three ropes in the figure are tied to a small, very light ring. Two of these ropes are anchored to walls at right angles with tensions T1 = 60 N and T2 = 95 N. What are the magnitude and direction of the tension 3 in the third rope? Figure Ex5.2

[112] N [57.7]° (below the positive x-axis) 6. Knight 5.005. [370368] Show Details In each of the two free-body diagrams, the forces are acting on a 2.4 kg object. For each diagram, find the values of ax and ay, the x and y components of the acceleration.

Figure Ex5.5

(a) [0.833] m/s2 [0] m/s2

(b) [0.833] m/s2 [0] m/s2

7. Knight 5.010. [370361] Show Details A 31 kg box hangs from a rope. What is the tension in the rope if the following are true? (a) The box is at rest? [304] N (b) The box moves up a steady 5.0 m/s? [304] N 2 (c) The box has vy = 5.0 m/s and is speeding up at 5.0 m/s ? [459] N 2 (d) The box has vy = 5.0 m/s and is slowing down at 5.0 m/s ? [149] N

8. Knight 5.013. [370363] Show Details It takes the elevator in a skyscraper 4.0 s to reach its cruising speed of 10 m/s. A 75 kg passenger gets aboard on the ground floor. What is the passenger's apparent weight at each of the following times? (a) before the elevator starts moving [735] N (b) while the elevator is speeding up [922] N (c) after the elevator reaches its cruising speed [735] N

9. Knight 5.025. [484206] Show Details A 5.8 kg object initially at rest at the origin is subjected to the time-varying force shown in Figure P5.25, with the vertical axis in 5 N increments. What is the object's velocity at t = 6 s? [3.45] m/s

10. Knight 5.027. [370364] Show Details A 1300 kg steel beam is supported by two ropes. Each rope has a maximum sustained tension of 6200 N.

Figure P5.27

Does either rope break? If so, which one(s)? [x] rope 1 [_] rope 2 [_] none

What is the tension in each rope?

rope 1 [8320] N

rope 2 [5690] N

11. Knight 5.028. [484196] Show Details A 465 kg piano is being lowered into position by a crane while two people steady it with ropes pulling to the sides. Bob's rope pulls to the left, 15° below horizontal, with 500 N of tension. Ellen's rope pulls toward the right, 25° below horizontal. (a) What tension must Ellen maintain in her rope to keep the piano descending at a steady speed? [533] N (b) What is the tension in the main cable supporting the piano? [4910] N

12. Knight 5.051. [484201] Show Details A m = 2.3 kg wood box slides down a vertical wood wall while you push on it at a = 50° angle. What magnitude of force should you apply to cause the box to slide down at a constant speed? [25.2] N

13. Knight 5.049. [454983] Show Details A pickup truck with a steel bed is carrying a steel file cabinet. If the truck's speed is 20 m/s, what is the shortest distance in which it can stop without the file cabinet sliding? (Use µs = 0.8 for the coefficient of static friction of steel on steel.) [25.5] m 14. Knight 5.045. [454936] Show Details A 2.4 kg wood block is launched up a wooden ramp that is inclined at a 22° angle. The block's initial speed is 11 m/s. (Use µk = 0.20 for the coefficient of kinetic friction for wood on wood.) (a) What vertical height does the block reach above its starting point? [4.13] m (b) What speed does it have when it slides back down to its starting point? [6.39] m/s down the ramp

15. Knight 5.031. [454958] Show Details Zach, whose mass is 79 kg, is in an elevator descending at 11 m/s. The elevator takes 3.4 s to brake to a stop at the first floor. (a) What is Zach's apparent weight before the elevator starts braking? [774] N (b) What is Zach's apparent weight while the elevator is braking? [1030] N

16. Knight 5.039. [484198] Show Details A 2.9 kg steel block is at rest on a steel table. A horizontal string pulls on the block. (a) What is the minimum string tension needed to move the block? [22.7] N (b) If the string tension is 29 N, what is the block's speed after moving 1.0 m? [2.87] m/s (c) If the string tension is 29 N and the table is coated with oil, what is the block's speed after moving 1.0 m? [4.36] m/s