Problem 1:
Running on soft dry sand is exhausting, so you switch to running on hard wet sand. The hard wet sand removes less energy from you because it
Answer: (A) barely moves downward as you push downward on it, so you do almost zero work on it. [60.5% picked]
Why: TBA
Problem 2:
You and seven of your teammates are rowing in a boat race and are heading northward toward the finish line. During each stroke, you immerse the blade (flat surface) of your oar (long stick used to propel the boat) in the water and make that blade move rapidly southward through the water. As the blade moves through the water, your boat accelerates northward because
Answer: (D) the water exerts a northward drag force on the southward-moving blade. [68.8% picked]
Why: TBA
Problem 3:
If a golf ball were smooth rather than dimpled, it would
Answer: (C) not travel as far after being hit by a golf club. [97.0% picked]
Why: TBA
Problem 4:
Flowing honey is less likely to become turbulent than flowing water because
Answer: (C) honey's much larger viscosity favors orderly laminar flow. [97.0% picked]
Why: TBA
Problem 5:
You are inflating a shiny plastic balloon with helium. The balloon starts as a thin, flat bag but it gradually gets thicker and rounder as it fills. At first, the thin plastic balloon doesn't float. But as you keep adding helium to the balloon and it gets thicker and rounder, it eventually begins floating because
Answer: (D) the weight of the helium-filled balloon increases as it fills, but the buoyant force it experiences increases much faster and eventually the buoyant force exceeds the balloon's weight. [54.0% picked]
Why: TBA
Problem 6:
Water hammer occurs when you suddenly stop the rapid flow of water in a pipe and results in the pipe-end experience a huge force in the direction of the water's original motion. It happens because flowing water has
Answer: (B) momentum. [59.3% picked]
Why: TBA
Problem 7:
The sculpture in a museum lobby includes a water fountain. Water flowing upward through a pipe passes through a short vertical nozzle and then rises to a height of 10 feet in the open air. As water flows along a streamline in this system, its energy changes forms several times. As water passes through the nozzle its energy transforms from
Answer: (D) pressure potential energy to kinetic energy and as it then rises to its peak height its energy transforms from kinetic energy to gravitational potential energy. [84.4% picked]
Why: TBA
Problem 8:
An airplane cruises forward at constant velocity through a region of calm, motionless air. After the plane has passed through that region of air, the air's total momentum is
Answer: (B) nonzero and directed exactly downward. [72.6% picked]
Why: TBA
Problem 9:
To avoid tipping over while turning right on a bicycle, why must you lean the bicycle toward your right?
Answer: (A) You accelerate rightward as you turn right and your inertia tends to make you tip over toward your left. By leaning toward your right, you cancel that tendency and avoid tipping over. [62.0% picked]
Why: TBA
Problem 10:
A tall flagpole is topped by a metal ball. When a large bird leaps off the ball, the flagpole starts bending back and forth rhythmically about its straight equilibrium shape. At what moment(s) during its rhythmic motion is the ball moving fastest?
Answer: (C) When the ball is coasting through equilibrium. [88.2% picked]
Why: TBA
Problem 11:
A 10-inch diameter wooden ball is floating on a calm fresh-water lake at sea level. The top of the ball is exactly 1 inch above the level of the water. When you transfer that ball to a fresh-water lake high up in the mountains, the ball
Answer: (B) floats deeper in the water, so that its top is less than 1 inch above the level of the water. [75.3% picked]
Why: TBA
Problem 12:
You are an astronaut spacewalking independently near your ship when you discover that your suit's propulsion system has failed. You and the ship are both coasting forward and are maintaining a constant separation of 100 feet (30 meters). There is danger in the distance, so you need to get to your ship. Fortunately, you have a hammer in your hand. To get to your ship, you throw the hammer
Answer: (D) away from the ship (in the direction that points from the ship to you). [89.4% picked]
Why: TBA
Problem 13:
An enormous asteroid is coasting straight toward your space station. With impact exactly 100 hours away, you use a tiny missile to blow the asteroid into two equal pieces. The space station is saved! Neglecting gravity and the tiny momentum of the tiny missile, what happens to the asteroid's total momentum and center of mass after the missile explosion?
Answer: (B) The asteroid's total momentum remains unchanged after the explosion and its center of mass passes through the space station exactly 100 hours later. [54.8% picked]
Why: TBA
Problem 14:
An toddler's sipping cup has a round base (like the bottom half of a ball) that is weighed so that the cup always returns to upright after being tipped. The cup is in a stable equilibrium when it is upright and tipping it causes its total
Answer: (C) potential energy to increase. [66.9% picked]
Why: TBA
Problem 15:
When water flows around a bend in a garden hose, the water pressure
Answer: (D) decreases near the inside of the curve and increases near the outside of the curve. [95.1% picked]
Why: TBA
Problem 16:
When you drop coins on a hard level surface, they sometimes roll for amazingly long time. Why does a rolling coin tend to stay upright for such a long time?
Answer: (C) The rolling coin naturally steers so as to place its contact point with the ground directly under its center of gravity. [96.2% picked]
Why: TBA
Problem 17:
You are designing a chair for a museum. While your chair will be a work of art, it must also be practical and it mustn't tip over easily. To ensure that it stays upright, you design it so that its
Answer: (C) center of gravity always rises if you tip it. [93.9% picked]
Why: TBA
Problem 18:
Firefighters are battling a fire on the 10th floor of an apartment building. When they stand on the ground, the steady stream of water from the short nozzle of their short fire hose rises vertically upward but reaches its peak height at only the 8th floor. Fortunately, they have a well-equipped fire truck with a longer hose, a longer nozzle, a more powerful pump, and a tall ladder. Which of these four tools could allow the firefighters to send a steady stream of water onto the 10th-floor fire?
Answer: (B) The more powerful pump [93.9% picked]
Why: TBA
Problem 19:
You are jumping up and down on a trampoline. As you drop from great height onto the trampoline's surface, when is the first moment that your speed stops increasing?
Answer: (B) When you reach equilibrium in the dented trampoline's surface. [82.1% picked]
Why: TBA
Problem 20:
A helium-filled balloon weighs only about 1/7th as much as the air it displaces. If you replace the helium gas in the balloon with hydrogen gas (which is half as dense as helium gas), the upward buoyant force on the balloon would
Answer: (A) stay the same and the net force on the balloon would increase slightly in the upward direction. [26.6% picked]
Why: TBA
Problem 21:
You are trying to increase the pressure in your village's water distribution system by modifying the local water tower. You should make that water tower
Answer: (C) taller (increase its altitude). [96.6% picked]
Why: TBA
Problem 22:
You are practicing tennis alone by hitting a tennis ball forward toward a cement wall. Each time the ball hits the wall, it bounces backward at high speed so that you can hit it again. During its bounce, the ball
Answer: (D) retains approximately all of its energy but transfers more forward momentum than it had to the wall. [51.0% picked]
Why: TBA
Problem 23:
You are standing in the middle of a subway car that is moving forward at constant velocity when another passenger accidently spills an enormous container of olive oil. Suddenly, the floor cannot exert any frictional forces on your feet. Because nothing else is touching you, you
Answer: (A) remain in the middle of the subway car. [57.4% picked]
Why: TBA
Problem 24:
You forgot to tip the bartender who brought a Shirley Temple drink to your luxury hotel suite. So you're leaning out over the balcony of your 20th floor suite and dropping solid gold marbles into the tip jar on the ground floor patio bar. You notice that it takes 4 seconds for each marble to fall into the jar, 20 floors below. When each marble has fallen for only 2 seconds, which floor of the hotel is it nearest? [Note: neglect any effects due to the air.]
Answer: (C) The marble is near the 15th floor. [86.3% picked]
Why: TBA
Problem 25:
Water is flowing gently out of the end of a garden hose. You block off most of the hose's opening with your thumb and now the water sprays out at high speed because you
Answer: (A) have slowed the water flow through hose and plumbing so that the water wastes less energy doing work against viscous forces. [30.8% picked]
Why: TBA
Problem 26:
You kick a soccer ball so that its path bends (curves) toward your left as it travels away from you and approaches the goal. The ball is able to bend its path (curve) toward your left because
Answer: (A) it is deflecting the airflow around it toward your right. [67.3% picked]
Why: TBA
Problem 27:
You are jogging northward along the ocean on a calm, windless day and are experiencing a pressure drag force that pushes you southward. The average velocity of the air a few feet behind you is
Answer: (C) directed northward. [81.0% picked]
Why: TBA
Problem 28:
You are cleaning your car with water from a hose and nozzle. At the center of the stream of water, right where it hits the side of your car, the water is almost coming to a complete stop. The pressure in the water at the center of the stream as it touches the car is
Answer: (D) higher than atmospheric pressure. [87.8% picked]
Why: TBA
Problem 29:
As air flows around a fast-moving ball, that air has difficulty maintaining laminar flow from the ball's sides to the ball's back. During the air's passage from sides to back, the pressure along each streamline
Answer: (A) increases and the airflow slows down. [52.9% picked]
Why: TBA
Problem 30:
You are riding a rollercoaster with a loop-the-loop. You have just rolled up the side of the loop and are, at this moment, exactly at the top of the loop. You and the car are upside down, yet you are pressed tightly into your seat. At this moment, you are accelerating
Answer: (D) downward at more than the acceleration due to gravity. [94.3% picked]
Why: TBA