Question 1

When sitting still on the ground, a tricycle is in a state of

Accepted Answer

A tricycle sitting still on the ground is not moving, so it is in a state of static equilibrium. It is stable because, if slightly disturbed (pushed or pulled), it will return to its original position without tipping over.

Question 2

When moving, a bicycle is in a state of dynamic equilibrium due to

Accepted Answer

Dynamic equilibrium in a moving bicycle is primarily due to gyroscopic effects from the spinning wheels and the shape of the fork, which affects the steering and stability.

Question 3

A three - wheeler is

Accepted Answer

A three-wheeler is statically stable because it can stand on its own without falling over, but it is dynamically unstable because it can easily tip over when in motion, especially during turns or under uneven loads.

Question 4

A motorcycle is

Accepted Answer

A motorcycle is statically unstable because it cannot stand up on its own without falling over, but it is dynamically stable when in motion, as the gyroscopic effect of the wheels and the ability to steer provide stability.

Question 5

In studying many martial arts, it is necessary to practice efficient and safe postures. One important concept related to how one should stand is that the feet should be reasonably far apart, because

Accepted Answer

The wider stance increases the base of support, which helps in stabilizing the person by distributing their weight over a larger area, thus improving balance and stability during martial arts practice.

Question 6

At various times in the news it has been reported that certain vehicles are susceptible to rolling over. The physical mechanism that is responsible for rollovers is

Accepted Answer

The correct mechanism for vehicle rollovers involves frictional torques from the road on the vehicle (in this case, a tricycle) about its center of mass. If the center of mass is high or if the vehicle takes a turn too quickly, the frictional force can create a torque that tips the vehicle over. This is why a lower center of mass in vehicles is often associated with better stability and less risk of rollover. Choices A, B, and D do not accurately describe the physics behind vehicle rollovers.

Question 7

It is important for cyclists to lean their bicycles while negotiating sharp turns because

Accepted Answer

Leaning into a turn helps cyclists balance the torque created by the frictional force from the road, which acts to push the bike and rider to the outside of the turn, with the gravitational force. This balance prevents them from flipping over.

Question 8

You are riding a multi-speed bicycle up a steep hill that's 100 m high and want to do as little work as possible on your way up the hill.

Accepted Answer

The answer of You are riding a multi-speed bicycle up...

Question 9

You buy an older motorcycle and notice that, even in low gear, it is difficult to get the bike going. You should replace the sprocket in the rear wheel with one that is

Accepted Answer

A larger rear sprocket increases the gear ratio, which reduces the amount of work the motor has to do to start moving, making it easier to get the bike going from a stop.

Question 10

You go to a quick - fix garage to get your brakes worked on. When your tires are re - installed, the mechanic forgets to put the lug nuts on your tires. Although nobody gets hurt, a tire comes off your car when you are traveling fairly rapidly and it is able to roll through a very large distance, even hitting bumps and objects in the way. Please explain why the tire can roll so far without tipping over.

Accepted Answer

The answer of You go to a quick - fix...

Question 11

Please explain why tricycles are better at sitting still than bicycles are, but bikes are the vehicles of choice when you want to be moving.

Accepted Answer

The answer of Please explain why tricycles are better at...

Question 12

Why does a skateboarder lean while negotiating a curve?

Accepted Answer

Leaning into a curve helps a skateboarder maintain balance by ensuring the net force (centripetal force) acts through their center of mass towards the center of the curve, preventing them from tipping over.

Question 13

A top is

Accepted Answer

A top is statically unstable because it cannot maintain its balance when not spinning, but it becomes dynamically stable when spinning due to the gyroscopic effect, which helps it maintain its orientation.

Question 14

An object is in stable equilibrium only when

Accepted Answer

An object is in stable equilibrium when its total potential energy is at a minimum, meaning that if it were to be slightly reoriented, its potential energy would increase. This characteristic ensures that the object returns to its equilibrium position after a slight disturbance.

Question 15

You can make a bicycle lean by

Accepted Answer

Briefly steering a bicycle in the direction opposite the turn (countersteering) initiates a lean towards the direction of the turn, which is necessary for making the turn. This is due to the principles of angular momentum and the conservation of angular momentum, which cause the bike to lean in the opposite direction of the initial steering input.

Question 16

What is one advantage and one drawback of a very large wheel on a bicycle or tricycle whose operator can pedal the front wheel?

Accepted Answer

The answer of What is one advantage and one drawback...

Question 17

What are three drawbacks to a bicycle or tricycle whose front wheel can be pedaled?

Accepted Answer

The answer of What are three drawbacks to a bicycle...

Question 18

Astronauts in the space shuttle feel weightless because

Accepted Answer

Astronauts feel weightless because they are in a constant state of free-fall towards Earth. The space shuttle orbits Earth in a continuous free-fall, creating the sensation of weightlessness.

Question 19

Escape velocity at the surface of the Earth is about

Accepted Answer

The escape velocity at the surface of the Earth is approximately 25,000 mph, which is the speed needed to break free from Earth's gravitational pull without any additional propulsion.

Question 20

What is the gravitational force that two 100 kg persons exert on each other when standing 1m apart?

Accepted Answer

The gravitational force between two masses is calculated using Newton's law of universal gravitation: F = G * (m1 * m2) / r^2. Here, G is the gravitational constant (6.674x10^-11 N(m/kg)^2), m1 and m2 are the masses (100 kg each), and r is the distance (1 m). Plugging in these values gives approximately 6.672x10^-7 N.

Quiz 4: Mechanical Objects, Part 2