91影视

A small compact car is pushing a large van that has broken down, and they travel along the road with equal velocities and accelerations. While the car is speeding up, is the force it exerts on the van larger than, smaller than, or the same magnitude as the force the van exerts on it? Which vehicle has the larger net force on it, or are the net forces the same? Explain.

When a smooth-flowing stream of water comes out of a faucet, it narrows as it falls. Explain

The dwarf planet Pluto has an elliptical orbit with a semi-major axis of $\mathbf{5}.\mathbf{91}脳{\mathbf{10}}^{12}\text{鈥�}\mathbf{m}$and eccentricity $\mathbf{0}.\mathbf{249}$.

(a) Calculate Pluto鈥檚 orbital period. Express your answer in seconds and in earth years.

(b) During Pluto鈥檚 orbit around the sun, what are its closest and farthest distances from the sun?

At its Ames Research Center, NASA uses its large "20-G"centrifuge to test the effects of very large accelerations (鈥渉yper gravity鈥�) on test pilots and astronauts. In this device, an arm 8.84 m long rotates about one end in a horizontal plane, and an astronaut is strapped in at the other end. Suppose that he is aligned along the centrifuge鈥檚 arm with his head at the outermost end. The maximum sustained acceleration to which humans are subjected in this device is typically 12.5 g. (a) How fast must the astronaut鈥檚 head be moving to experience this maximum acceleration? (b) What is the difference between the acceleration of his head and feet if the astronaut is 2.00 m tall? (c) How fast in rpm rpm 1 rev/min² is the arm turning to produce the maximum sustained acceleration?

Calculate the moment of inertia of each of the following uniform objects about the axes indicated. Consult Table 9.2 as needed.

(a) A thin 2.50-kg rod of length 75.0 cm, about an axis perpendicular to it and passing through (i) one end and (ii) its center, and (iii) about an axis parallel to the rod and passing through it.

(b) A 3.00-kg sphere 38.0 cm in diameter, about an axis through its center, if the sphere is (i) solid and (ii) a thin-walled hollow shell.

(c) An 8.00-kg cylinder, of length 19.5 cm and diameter 12.0 cm, about the central axis of the cylinder, if the cylinder is (i) thin-walled and hollow, and (ii) solid.

Vector $A$has y-component $Ay=+9.60m$. A makes an angle of $32.0$ counterclockwise from the +y-axis. (a) What is the x-component of $A$ ? (b) What is the magnitude of $A$ ?

A 0.500-kg glider, attached to the end of an ideal spring with force constant k = 450 N/m, undergoes SHM with an amplitude of 0.040 m. Compute (a) the maximum speed of the glider; (b) the speed of the glider when it is at x = -0.015 m; (c) the magnitude of the maximum acceleration of the glider; (d) the acceleration of the glider at x = -0.015 m; (e) the total mechanical energy of the glider at any point in its motion.

A chair of mass $\mathbf{12}\mathbf{.}\mathbf{0}\mathbf{}\mathbf{kg}$is sitting on the horizontal floor; the floor is not frictionless. You push on the chair with a force $\mathbf{F}\mathbf{=}\mathbf{40}\mathbf{.}\mathbf{0}\mathbf{鈥�}\mathbf{N}$that is directed at an angle of $\mathbf{37}\mathbf{.}\mathbf{0}\mathbf{掳}$below the horizontal, and the chair slides along the floor. (a) Draw a clearly labeled free-body diagram for the chair. (b) Use your diagram and Newton鈥檚 laws to calculate the normal force that the floor exerts on the chair.

A 45.0-kg crate of tools rests on a horizontal floor. You exert a gradually increasing horizontal push on it, and the crate just begins to move when your force exceeds 313 N. Then you must reduce your push to 208 N to keep it moving at a steady 25.0 m/s . (a) What are the coefficients of static and kinetic friction between the crate and the floor? (b) What push must you exert to give it an acceleration of $\mathbf{1}\mathbf{.}\mathbf{10}\mathbf{}\mathbf{m}\mathbf{/}{\mathbf{s}}^{\mathbf{2}}$? (c) Suppose you were performing the same experiment on the moon, where the acceleration due to gravity is $\mathbf{1}\mathbf{.}\mathbf{62}\mathbf{}\mathbf{m}\mathbf{/}{\mathbf{s}}^{\mathbf{2}}$. (i) What magnitude push would cause it to move? (ii) What would its acceleration be if you maintained the push in part (b)?

You (mass $\mathbf{55}\mathbf{kg}$) are riding a frictionless skateboard (mass $\mathbf{5}\mathbf{.}\mathbf{0}\mathbf{kg}$) in a straight line at a speed of role="math" localid="1660158581290" $\mathbf{4}\mathbf{.}\mathbf{5}\mathbf{}\raisebox{1ex}{${\displaystyle \text{m}}$}\!\left/ \!\raisebox{-1ex}{${\displaystyle \text{s}}$}\right.$. A friend standing on a balcony above you drops a $\mathbf{2}\mathbf{.}\mathbf{5}\mathbf{\text{kg}}$ sack of flour straight down into your arms. (a) What is your new speed while you hold the sack? (b) Since the sack was dropped vertically, how can it affect your horizontal motion? Explain. (c) Now you try to rid yourself of the extra weight by throwing the sack straight up. What will be your speed while the sack is in the air? Explain.