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# Mechanics : Newton's Laws of Motion

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I need help with the following conceptual questions and the problems numbered 2, 4, 32, 36, 38.

1. A friend tells you that since his car is at rest there are no forces acting on it. How would you reply?

6. Riding in an elevator moving with a constant speed, you begin a game of darts. Do you have to aim your darts higher,
lower or the same as when you play darts on solid ground?

20. A surfer hangs ten and acc down the sloping face of a wave. If the surfer acceleration is 3.25 m/s2 and the friction
can be ignored, what is the angle at which the face of the wave is inclined above the horizontal?

25. A 65kg skier speeds down a trail, the surface is smooth and inclined at an 22 degrees with the horizontal.

(a) Find the direction and magnitude of the net force acting on the skier.
(b) Does the net force exerted on the skier increase, decrease, or stay the same as the slope becomes steeper?

37. A 23 kg suitcase is being pulled with constant speed by a handle that is at an angle 25 degrees above the horizontal. If
the normal force exerted on the force is 180 N, what is the force F applied to the handle?

39. A 9.3 kg child sits in a 3.7 kg high chair.

(a) Draw a free body diagram for the child and find the normal force exerted by the chair on the chills.
(b) Draw a free body diagram for the chair and find the normal force exerted by the floor on the chair.

42. Find the normal force exerted on a 2.7 kg book resting on a surface inclined at 32 degrees above the horizontal.

(a) If the angle of the incline is reduced do you expect the normal force to Increase, decrease, or stay the same?

50. Biomechanical research has shown that when a 67 kg person is running, the force exerted on each foot as it strikes the
ground can be as great as 2300 N.

(a) What is the ratio of the force exerted on the foot by the ground to the person's body weight?
(b) If the only forces acting on the person are (i) the force exerted by the ground and (ii) the person's weight, what is
the magnitude and direction of the person's acceleration? C. If the acceleration found in part (b) acts 10.0 ms, what is
the resulting change in the vertical component of the person's velocity?