A car is moving forward slowly and speeding up. A student claims "the car exerts a force on itself" or "the car's engine exerts a force on the car." Argue that this idea cannot be accurate and that friction exerted by the road is the propulsive force on the car. Make your evidence and reasoning as persuasive as possible. Is it static or kinetic friction? Suggestions: Consider a road covered with light gravel. Consider a sharp print of the tire tread on an asphalt road, obtained by coating the tread with dust

Determine the order of magnitude of the gravitational force that you exert on another person 2 m away. In your solution, state the quantities you measure or estimate and their values.

Your little sister (mass $25.0 \mathrm{~kg}$ ) is sitting in her little red wagon (mass $8.50 \mathrm{~kg}$ ) at rest. You begin pulling her forward and continue accelerating her with a constant force for $2.35 \mathrm{~s}$, at the end of which time she's moving at a speed of $1.80 \mathrm{~m} / \mathrm{s}$.
(a) Calculate the impulse you imparted to the wagon and its passenger.
(b) With what force did you pull on the wagon?

Cargo is tied with rope on the roof of a 4.5-foot-tall car. The car is traveling down a road at 42 mph and hits a concrete barrier. The rope snaps, allowing the cargo to propel forward. Use the equations $y=-16.1 t^{2}+4.75$ and $y=-0.0042 x^{2}+4.75$ where y represents height in feet, x represents horizontal distance in feet, and t represents time in seconds, to find the time it takes for the cargo to hit the ground and the horizontal distance it travels.

The spring has a stiffness k = 50 lb/ft and an unstretched length of 2 ft. As shown, it is confined by the plate and wall using cables so that its length is 1.5 ft. A 4-lb block is given a speed $v_A$ when it is at A, and it slides down the incline having a coefficient of kinetic friction $\mu_k = 0.2$. If it strikes the plate and pushes it forward 0.25 ft before stopping, determine its speed at A. Neglect the mass of the plate and spring.

The gas-phase reaction between hydrogen and iodine

$$\mathrm{H}_2(g)+\mathrm{I}_2(g) \rightleftharpoons 2 \mathrm{HI}(g)$$

proceeds with a rate constant for the forward reaction at $700^{\circ} \mathrm{C}$ of $138 \mathrm{~L} / \mathrm{mol} \cdot \mathrm{s}$ and an activation energy of $165 \mathrm{~kJ} / \mathrm{mol}$. (a) Calculate the activation energy of the reverse reaction given that $\Delta H_{\mathrm{f}}^{\circ}$ for $\mathrm{HI}$ is $26.48 \mathrm{~kJ} / \mathrm{mol}$ and $\Delta H_{\mathrm{f}}{ }^{\circ}$ for $\mathrm{I}_2(\mathrm{~g})$ is $62.44 \mathrm{~kJ} / \mathrm{mol}$. (b) Calculate the rate constant for the reverse reaction at $700^{\circ} \mathrm{C}$. (Assume $\mathrm{A}$ in the equation $k=\mathrm{Ae}^{-E_{\mathrm{a}} / R T}$ is the same for both forward and reverse reactions.) (c) Calculate the rate of the reverse reaction if the concentration of $\mathrm{HI}$ is $0.200 \mathrm{M}$. The reverse reaction is second-order in HI.

The Latin root -jec-means "thro w." This root is found in many scientific words, such as conjecture, which means "to guess by 'throwing' facts or inferences together."
Choose the letter of the best definition for the given word below. " project": a. to "throw" forward b. to "throw" into c. to "throw" out of d. object designed to be "thrown" or shot e. path along which an object is "thrown" f. "thrown" away; hopeless g. state of being "thrown" down; depression h. "throw" back at

Weddell seals foraging in open water dive toward the ocean bottom by swimming forward in a straight-line path tipped below the horizontal. The tracking data for one seal showed it taking 4.0 min to descend 360 m below the surface while moving 920 m horizontally. a. What was the angle of the seal's path below the horizontal? b. What distance did the seal cover in making this dive? c. What was the seal's speed, in m/s?

When run at maximum power output, the motor in a self-propelled tank car can accelerate the full car (mass $M$ kg) along a horizontal track at $a$ m/s$^2$ . The tank is full at time zero, but the contents pour out of a hole in the bottom at rate $k$ kg/s thereafter. If the car is at rest at time zero and full forward power is turned on at that time , how fast will it be moving at any time $t$ before the tank is empty?

Consider the equation for acetic acid plus water. Use the table "Relative Strengths of Acids and Bases," earlier in this chapter, to answer the questions below.

$$\mathrm{CH}_3 \mathrm{COOH}+\mathrm{H}_2 \mathrm{O} \rightleftarrows \mathrm{CH}_3 \mathrm{COO}^{-}+\mathrm{H}_3 \mathrm{O}^{+}$$

a. Compare the strength of the two acids.

b. Compare the strength of the two bases.

c. Which direction, forward or reverse, is favored for this reaction?

Squid use jet propulsion for rapid escapes. A squid pulls water into its body and then rapidly ejects the water backward to propel itself forward. A 1.5 kg squid (not including water mass) can accelerate at $20 \mathrm { m } / \mathrm { s } ^ { 2 }$ by ejecting 0.15 kg of water. a. What is the magnitude of the thrust force on the squid? b. What is the magnitude of the force on the water being ejected? c. What acceleration is experienced by the water?

Particles of mud are thrown from the rim of a rolling wheel. If the forward speed of the wheel is $v_{0}$, and the radius of the wheel is b, show that the greatest height above the ground that the mud can go is $b+\frac{v_{0}^{2}}{2 g}+\frac{g b^{2}}{2 v_{0}^{2}}$ At what point on the rolling wheel does this mud leave? (Note: It is necessary to assume that $v_{0}^{2} \geq b g$.)

The Latin root -jec-means "thro w." This root is found in many scientific words, such as conjecture, which means "to guess by 'throwing' facts or inferences together."
Choose the letter of the best definition for the given word below. "deject ": a. to "throw" forward b. to "throw" into c. to "throw" out of d. object designed to be "thrown" or shot e. path along which an object is "thrown" f. "thrown" away; hopeless g. state of being "thrown" down; depression h. "throw" back at

Squids can move through the water using a form of jet propulsion. Suppose a squid jets forward from rest with constant acceleration for $0.170 \mathrm{~s}$, moving through a distance of $0.179 \mathrm{~m}$. The squid then turns off its jets and coasts to rest with constant acceleration. The total time for this motion (from rest to rest) is $0.400 \mathrm{~s}$, and the total distance covered is $0.421 \mathrm{~m}$. What is the magnitude of the squid's acceleration during the time it is jetting?