Re: [作業] 誰能po一下物理題目= =我忘記帶課本回家
3-38 An airplane is flying horizontally with a constant velocity.
The propellers are pushing backward on the air.
(a)Is the airplane in equilibrium ?
(b)What forces are acting in the horizontal plane ?
3-58 When a rocket ship is at a distance R from the surface of the earth,
the earth's gravitational attraction on the ship is 144,000 N.
What is the erath's gravitational attraction when the ship is at a
distance 3R from the surface ?(R is the radius of the earth )
3-72 An astronaut of mass m is in a spaceship that takes off straight up
from the surface of the earth. Its acceleration is kept equal to
9.8 m/s*2
(a)What is the effective weight of the astronaut just after takeoff ?
(b)What is his effective weight when the spaceship is at a distance
from the surface of the earth equal to the radius of the earth ?
3-80 A stone boat of total weight 60,000 N is used in a horse-pulling
contest. The coefficient of satic friction between the stone boat
and the earth is 0.6, and the coefficient of sliding friction is 0.4.
(a)What force must a pair of horses exert to start the stone boat
moving ?
(b)What force must the horses exert to keep the stone boat moving at
a constant velocity?
3-86 A runner's foot strikes the ground with a velocity of 10 m/s downward.
If the effective mass of the foot and leg that is brought to rest is
9 kg, what is the force on the foot as it comes to rest with constant
acceleration in
(a)0.03m on a soft surface
(b)0.005m on a hard surface
打完啦！好累！有錯請更正喔！
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