A force of 5.3 N is needed to hold on to an umbrella in a strong wind. If the air molecules each have a mass of 4.7 ×10-26 kg,
and each one strikes the umbrella (without rebounding) with a speed of 2.0 m/s in the same direction, how many molecules strike the umbrella each second? Assume that the wind blows horizontally so that the gravitational force exerted on the air molecules can be neglected.
5.6 ×1025 per second
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Projectile Motion: An athlete participates in an interplanetary discus throw competition during an Olympiad that takes place on a planet where the acceleration due to gravity is 9.7 m/s2. He throws the discus with an initial velocity of 20 m/s at an angle of 60° from the vertical. Neglecting air resistance and the height of the discus at the point of release, what is the range of the discus?
A. 21 m B. 60 m C. 36 m D. 40 m E. 32 m
Suppose that a ship is accelerating through space in such a way that the passengers are experiencing a constant force (due to the thrust of the ship) equivalent to the total weight of the ship and passengers on Earth
From the point of view of observers on Earth, how does the ship accelerate? A) It has a constant acceleration of 9.8 m/s2, therefore increasing its speed by 9.8 m/s with each passing second. B) At first, it has a nearly constant acceleration of 9.8 m/ s2. But as it approaches the speed of light, its acceleration gradually slows in such a way that it never stops accelerating, but never reaches the speed of light either. C) At first, it has a very large acceleration—much larger than 9.8 m/s2. But when it reaches the speed of light it stops accelerating. D) It has a constant acceleration of 9.8 m/s2 until it reaches a speed of half the speed of light. Then its acceleration suddenly slows so that it can't go much faster.
Suppose an automobile's fuel could be made to burn hotter without harming the engine's operation. Would you still get the same amount of useful work from each gallon of gasoline?
A) It wouldn't make any difference, because the efficiency is related only to the amount of input energy, and not to the temperature of this energy. B) You would get more work, because heat engines are more efficient at converting chemical energy into thermal energy when the temperature is higher. C) You would get more work, because heat engines are more efficient at converting thermal energy into work when the input temperature is higher. D) You would get less work, because heat engines run less efficiently when the input temperature is higher. E) You would get less work, because less chemical energy would be used at the higher temperature.
Identical balls oscillate with the same period T on Earth. Ball A is attached to an ideal spring and ball B swings back and forth to form a simple pendulum. These systems are now taken to the Moon, where g = 1.6 m/s2, and set into oscillation
Which of the following statements about these systems are true? (There could be more than one correct choice.) A) Both systems will have the same period on the Moon as on Earth. B) On the Moon, ball A will take longer to complete one cycle than ball B. C) On the Moon, ball B will take longer to complete one cycle than ball A. D) On the Moon, ball A will execute more vibrations each minute than ball B. E) On the Moon, ball B will execute more vibrations each minute than ball A.