Physics Test Chapter 4
In another solar system a planet has twice the earth's mass and three times the earth's radius. Compare your weight on this planet with your earth-weight. Assume that the masses of the earth and of the other planet are uniformly distributed.
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An airboat with mass 3.50 x 10^2 kg, including passengers, has an engine that produces a net horizontal force of 7.70 x 10^2 N, after accounting for forces of resistance. (a) Find the acceleration of the airboat. (b) Starting from rest, how long does it take the ariboat to reach a speed of 12.0 m/s?
A) F = ma 7.70 x 10^2 N = 3.50 x 10^2 kg x a a = 2.2 m/s^2 B) a = v/t 2.2 m/s^2 = 12 m/s / t t = 5.5 seconds
A rope is used in a tug-of-war between two teams of five people each. Both teams are equally strong, so neither team wins. An identical rope is tied to a tree, and the same ten people just as hard on the loose end as they did in the contest. In both cases, the people pull steadily with no jerking. Which rope sustains the greater tension, A) The rope tied to a tree B) The rope in the tug-of-war C) The ropes sustain the same tension
A) The rope tied to the tree
In which one of the following situations could an object possibly be in equilibrium? A) Three forces act on the object; the forces all point along the same line but may have different directions B) Two perpendicular forces act on the object C) A single force acts on the object D) In none of the situation described in (a), (b), and (c) could the object possibly be in equilibrium.
A) Three forces act on the object; the forces all point along the same line but may have different directions
An object is moving at a constant velocity. All but one of the following statements could be true. Which one cannot be true? A) No forces act on the object. B) A single force acts on the object. C) Two forces act simultaneously on the object. D) Three forces act simultaneously on the object.
B) A single force acts on the object.
All of the following, except one, cause the acceleration of an object to double. Which one is the exception? A) All forces acting on the object double. B) The net force acting on the object doubles. C) Both the net force acting on the object and the mass of the object double. D) The net force acting on the object remains the same, while the mass of the object is reduced by a factor of two.
C) Both the net force acting on the object and the mass of the object double.
The net external force acting on an object is zero. Which one of the following statements is true? A) The object can only be stationary. B) The object can only be traveling with a constant velocity. C) The object can be either stationary or traveling with a constant velocity. D) The object can only be traveling with a velocity that is changing.
C) The object can be either stationary or traveling with a constant velocity.
If an object of mass m moves with constant velocity v, the net force on the object is A) mg is correct B) mv C) ma D) 0 E) None of these answers is correct.
C) ma
A cup of coffee is sitting on a table in a recreational vehicle (RV). The cup slides toward the rear of the RV. According to Newton's first law, which one or more of the following statements could describe the motion of the RV? A) The RV is at rest, and the driver suddenly accelerates. B) The RV is moving forward, and the driver suddenly accelerates. C) The RV is moving backward, and the driver suddenly hits the brakes. D) A and B E) A, B, and C
D) A and B
In Case A an object is moving straight downward with a constant speed of 9.80 m/s, while in Case B an object is moving straight downward with a constant acceleration of magnitude 9.80 m/s^2. Which one of the following is true? A) A nonzero net external force acts on the object in both cases. B) A nonzero external force acts on the object in neither case. C) A nonzero net external force acts on the object in Case A only. D) A nonzero net external force acts on the object in Case B only.
D) A nonzero net external force acts on the object in Case B only.
A father and his seven-year-old daughter are facing each other on ice skates. With their hands, they push off against one another. Which one or more of the following statements is (are) true? A) Each experience an acceleration that has a different magnitude B) Each experiences an acceleration of the same magnitude C) Each experiences a pushing force that has a different magnitude D) Each experiences a pushing force that has the same magnitude
D) Each experiences a pushing force that has the same magnitude
During the final stages of descent, a sky diver with an open parachute approaches the ground with a constant velocity. There is no wind to blow him from side. Which one of the following statements is true? A) The sky diver is not in equilibrium B) The force of gravity is the only force acting on the sky diver, so that he is in equilibrium C) The sky diver is in equilibrium because no forces are acting on him. D) The sky diver is in equilibrium because two forces act on him, the downward acting force of gravity and the upward acting force of the parachute.
D) The sky diver is in equilibrium because two forces act on him, the downward acting force of gravity and the upward acting force of the parachute.
Which of the following is true, according to Newton's laws of motion? Ignore friction. A) A sports utility vehicle hits a stationary motorcycle. Since it is stationary, the motorcycle sustains a greater than the SUV does. B) A semitrailer truck crashes all the way through a wall. Since the wall collapses, the wall sustains a greater force than the truck does. C) Sam (18 years old) and his sister (9 years old) go ice skating. They push off against each other and fly apart. Sam flies off with the greater acceleration. D) Two astronauts on a space walk are throwing a ball back and forth between each other. In this game of catch the distance between them remains constant. E) None of the above is true, according to the third law.
E) None of the above is true, according to the third law.
An astronaut applies a force of 500 N to an asteroid, and it accelerates at 3.00 m/s^2. What is the asteroid's mass?
F = ma 500 N = m x 3.00 m/s^2 m = 166.67 kg
A 7.0 kg bowling ball experiences a net force of 6.0 N. What will be its acceleration?
F = ma 6.0 N = 7.0 kg x a a = 0.857 m/s^2
A sled is tied to a tree on a frictionless, snow-covered hill, as shown in figure 4.13a. If the sled weighs 77.0 N, find the force exerted by the rope on the sled and the magnitude of the normal force n exerted by the hill on the sled.
F = may Fn - fg (cos 30) = 0 Fn = fg (cos 30) = 66.7 N F = max Fn - fg (sin 30) = 0 Fn = fg (sin 30) = 38.9 N
A traffic light weighing 1.00 x 10^2 N hangs from a vertical cable tied to two other cables that are fastened to a support, as in figure. The upper cables make angles of 37.0 and 53.0 with the horizontal. Find the tension in each of the three cables.
Fx = max T2 (cos 53) - T1 (cos 37) = 0 T2 (cos 53) = T1 (cos 37) T2 = T1 (cos 37) / (cos 53) = 1.33T1 T2 = 1.33 T1 ---- 1.33 x 60 N = 79 N Fy = may T1 (sin 37) = T2 (sin 53) - T3 = 0 T1 (sin 37) + (1.33 T1) sin 53 - 100 N = 0 T1 = 60 N and T3 = 100 N
Two horses are pulling a barge with mass 2.00 x 10^3 kg along a canal, as shown in the figure. The cable connected to the first horse makes an angle of 30.0 with respect to the direction of the canal, while the cable connected to the barge, starting at rest, if each horse exerts a force of magnitude 6.00 x 10^2 N on the barge, ignore forces of resistance on the barge.
Horse #1 x = 600 N x (cos 30) = 519.6 N y = 600 N x (sin 30) = 300 N Horse #2 x= 600 N x (cos 45) = 424.3 n y = 600 N x (sin 45) = 424.3 N 519.6 + 424.3 = 943.9 N / 2000 = 0.47m/s^2 424.3 - 300 = 124.3 / 2000 = 0.06 m/s^2
A person has a choice of either pushing or pulling a sled at a constant velocity. friction is present. if the angle theta is the same in both cases, does it require less force to push or to pull the sled?
Less force to pull
A crate hangs from a ring in the middle of a rope, as the drawing illustrates. A person is pulling on the right end of the rope to keep the crate in equilibrium. Can the rope ever be made perfectly horizontal?
No because there is no force acting on the crate.
Newton's second law indicates that when a net force acts on an object, it must accelerate. Does this mean that when two or more forces are applied to an object simultaneously, it must accelerate?
No, the two forces may cancel each other out.
Three identical blocks are being pulled or pushed across a horizontal BB surface by a force F, as shown in the drawings. The force F in each case has the same magnitude. Rank the kinetic frictional forces that act on the blocks in ascending order (smallest first) A) B, C, A B) C, A, B C) B, A, C D) C, B, A E) A, C, B
Refer to drawings on paper C) B, A, C
Two objects with masses m1 and m2 are separated by a distance 2d. Mass m2 is greater than mass m1. A third object has a mass m3. All three objects are located on the same straight line. The net gravitational force acting on the third object is zero. Which one of the drawings correctly represents the locations of the objects?
Refer to packet for drawings. (D)
A man weighs a fish with a spring scale attached to the ceiling of an elevator, as shown in Figure (a). While the elevator is at rest, he measures a weight of 40.0 N. (a) What weight does the scale read if the elevator accelerates upward at 20.0 m/s^2, as in figure (b)? (c) If the elevator cable breaks, what does the scale read?
w = mg 40 N = m x 9.8 m = 4.08 A) Fn = Fg + ma Fn = 40 + 4.08(2) Fn = 48.16 N B) Fn = Fg - ma Fn = 40 - (4.08)(2) Fn = 31.84 N C) Fn = Fg - mg Fn = 0 N
Four forces act on an object, given by A = 40 N east, B = 50 N north, C = 70 N west, and D = 90 N south. What is the magnitude of the net force on the object?
√30² + 40² √2500 = 50 N
