Question 1

A fan attached to an ice sailcraft stalled on a windless day blows air into the sail that bounces backward upon impact.The boat

Accepted Answer

The answer of A fan attached to an ice sailcraft...

Question 2

When a boxer moves into an oncoming punch,the force experienced is

Accepted Answer

When a boxer moves into an oncoming punch, the force experienced is increased. This is because the punch is now adding its force to the boxer's own movement, resulting in a stronger impact. Choosing A or C is incorrect as they both suggest a decrease or no change in force, respectively. Choosing D is incorrect as there is no evidence to suggest that all three options are valid.

Question 3

When you jump from an elevated position you usually bend your knees upon reaching the ground.By doing this,the contact time is about 10 times more than for a stiff-legged landing and the average force your body experiences is reduced by

Accepted Answer

When you bend your knees upon reaching the ground, the contact time increases, which reduces the average force your body experiences. Studies have shown that the reduction in force is roughly proportional to the increase in contact time, with a factor of about 10. Therefore, the best choice is C, which states that the average force your body experiences is reduced by about 10 times.

Question 4

According to the impulse-momentum relationship Ft = change in mv,a falling bungee jumper has momentum which is reduced by the force F exerted by the bungee cord.If v is the speed of the jumper,then m in the equation is the mass of the

Accepted Answer

The impulse-momentum relationship is described by Ft = change in mv, where F represents the force, t represents time, m represents the mass of the object, and v represents the final velocity of the object after a certain time. In the case of a falling bungee jumper, the force exerted by the bungee cord reduces the momentum of the jumper. Therefore, the mass (m) in the equation refers to the mass of the jumper.

Question 5

Whether a truck comes to a stop by crashing into a haystack or a brick wall,the impulse is

Accepted Answer

Impulse is defined as the change in momentum of an object, which is the product of mass and velocity change. Whether a truck stops by hitting a haystack or a brick wall, the change in momentum (from its initial momentum to zero) is the same, hence the impulse is the same in both cases.

Question 6

A car traveling along the highway brakes to a stop.A greater braking force is required when the car has

Accepted Answer

The greater the mass and momentum of the car, the greater the force required to bring it to a stop. This is because both mass and momentum contribute to the car's overall inertia, which must be overcome by a braking force. Additionally, a shorter stopping distance requires a greater force to decelerate the car in a shorter amount of time. Therefore, all of the above choices are correct.

Question 7

Padded dashboards in cars are safer in an accident than non-padded ones because a person hitting the dash has

Accepted Answer

Padded dashboards increase the time of contact between a person's head and the dashboard, which reduces the contact force experienced by the head. Therefore, both choices A and B are correct.

Question 8

Which of these two collisions is more damaging; driving into a concrete wall with no "give," or colliding head-on with an identical car moving toward you at your same speed?

Accepted Answer

Both scenarios are equivalent in terms of the forces involved and the damage incurred. In both cases, the change in velocity and the forces experienced by the occupants would be the same, assuming all other factors are equal. This is because the relative velocity between the car and the wall or the two cars is the same, leading to similar energy dissipation requirements.

Question 9

Whether a truck comes to a stop by crashing into a haystack or a brick wall,the stopping force is

Accepted Answer

The stopping force is greater with the brick wall because it provides a greater resistance or frictional force compared to the relatively softer and pliable haystack.

Question 10

The conservation of momentum is most closely related to Newton's

Accepted Answer

The conservation of momentum is most closely related to Newton's third law, which states that for every action, there is an equal and opposite reaction. In other words, when two objects collide, the force exerted by one object on the other is equal in magnitude and opposite in direction to the force exerted by the other object on the first. This results in the conservation of momentum, as the momentum of the objects before the collision is equal to the momentum of the objects after the collision.

Question 11

A boxer punches a sheet of paper in midair from rest to a speed of 40 m/s in 0.05 s.If the mass of the paper is 0.01 kg,the force of the punch on the paper is

Accepted Answer

The force can be calculated using the formula F = ma, where a is the acceleration. First, find the acceleration using a = Δv/Δt = (40 m/s) / (0.05 s) = 800 m/s². Then, F = 0.01 kg * 800 m/s² = 8.0 N.

Question 12

A 1000-kg truck moving at 10 m/s that brakes to a stop in 5 s has an average braking force of

Accepted Answer

The average braking force can be calculated using the formula: Force = mass * acceleration. The acceleration can be found using the formula: acceleration = (final velocity - initial velocity) / time. Here, the initial velocity is 10 m/s, the final velocity is 0 m/s, and the time is 5 s. So, acceleration = (0 - 10) / 5 = -2 m/s². Therefore, the force = 1000 kg * (-2 m/s²) = -2000 N. The magnitude of the force is 2000 N.

Question 13

The greater efficiency achieved with the curved blades of a Pelton wheel is due to

Accepted Answer

The answer of The greater efficiency achieved with the curved...

Question 14

When you can't escape being hit by a fast-moving object,you'll suffer a smaller force if the collision time is

Accepted Answer

The longer the collision time, the more time the force has to act on the object, which reduces the overall force exerted. This is why car manufacturers design crumple zones that increase the collision time in the event of a crash, reducing the force experienced by passengers.

Question 15

The force of air impact upon the sail of a boat is greater if the air

Accepted Answer

The force of air impact upon the sail of a boat is greater if the air encounters the sail head-on. This is because when the air hits the sail head-on, it pushes it directly, creating a larger force. When the air encounters the sail at a grazing angle, it will still create some force but it will not be as much as when it is hitting the sail head-on. The option A is not possible as air cannot bounce upon impact as it is a fluid and does not have a solid surface.

Question 16

When a boxer is moving away from a punch,the force experienced is reduced because

Accepted Answer

When a boxer moves away from a punch, the time of contact between the punch and the boxer's body is increased. This means that the force is distributed over a longer period of time, thus reducing the impact force experienced by the boxer. However, momentum transfer and the effectiveness of the punch are not necessarily reduced.

Question 17

Compared with falling on a wooden floor,a wine glass may not break when it falls on a carpeted floor because of

Accepted Answer

A carpeted floor increases the time over which the stopping force acts, reducing the force and thus the likelihood of breaking.

Question 18

A karate chop is more effective if one's hand

Accepted Answer

The answer of A karate chop is more effective if...

Question 19

According to the impulse-momentum relationship Ft = change in mv,a falling baseball hits a player with a force F.The t in the equation is the time

Accepted Answer

The impulse-momentum relationship relates the force applied to an object to the change in its momentum. In this case, the force F is the force with which the baseball hits the player, and t refers to the time during which the force is applied, in other words, the time of contact between the ball and the player. Therefore, the correct answer is B - the time of contact of the ball hitting the player. The other choices are not relevant to the impulse-momentum relationship.

Question 20

A karate expert executes a swift blow and breaks a cement block with her bare hand.The magnitude of the force on her hand is

Accepted Answer

According to Newton's third law of motion, for every action, there is an equal and opposite reaction. Therefore, the force applied by the karate expert's hand on the cement block is equal in magnitude to the force exerted by the block on her hand.

Quiz 3: Momentum and Energy