1.
A .05 kg bullet is fired at a velocity of 500 m/s, and embeds itself in a block
of mass 4 kg, initially at rest and on a frictionless surface. What is the final
velocity of the block?
Correct Answer
A. 6.17 m/s
Explanation
When the bullet embeds itself in the block, the total momentum before the collision is equal to the total momentum after the collision. The momentum of the bullet before the collision is calculated by multiplying its mass (0.05 kg) by its velocity (500 m/s), which gives 25 kg*m/s. Since the block is initially at rest, its momentum before the collision is 0 kg*m/s. After the collision, the bullet and the block move together with a final velocity. Using the principle of conservation of momentum, the total momentum after the collision is equal to the total momentum before the collision. Therefore, the final velocity of the block can be calculated by dividing the total momentum (25 kg*m/s) by the mass of the block (4 kg), which gives 6.25 m/s. Rounding off to two decimal places, the final velocity of the block is 6.17 m/s.
2.
Momentum is
Correct Answer
B. Mass x velocity
Explanation
The correct answer is mass x velocity because momentum is defined as the product of an object's mass and its velocity. In other words, momentum is a measure of how much force is needed to stop an object or change its direction. The greater the mass or velocity of an object, the greater its momentum will be. Therefore, the formula for momentum is mass x velocity.
3.
Which of the following is not a simple machine?
Correct Answer
C. Typewriter
Explanation
The typewriter is not considered a simple machine because it does not have any mechanical advantage or fulfill the basic principles of a simple machine. Simple machines are typically defined as devices that make work easier by allowing a smaller force to be applied over a greater distance. While the typewriter may have some mechanical components, it does not fit the criteria of a simple machine.
4.
The unit for work
Correct Answer
B. Joules
Explanation
The unit for work is joules. Work is defined as the energy transferred to or from an object by the application of force along a displacement. Joules is the SI unit for energy, and it represents the amount of work done when a force of one newton is applied over a distance of one meter. Therefore, joules is the correct unit for measuring work.
5.
A form of energy that is transferred by a difference in temperature
Correct Answer
A. Thermal energy
Explanation
Thermal energy is the correct answer because it is a form of energy that is transferred between objects or systems due to a difference in temperature. When there is a temperature difference, heat flows from the object or system with higher temperature to the one with lower temperature, transferring thermal energy in the process. This energy can be measured in units such as calories or joules and is responsible for the sensation of warmth or coldness.
6.
Kinetic energy is maximum for a roller coaster
Correct Answer
A. At its lowest point
Explanation
The correct answer is "at its lowest point." At the lowest point of a roller coaster, it has the maximum kinetic energy because it has the maximum velocity. As the roller coaster descends from a higher point to a lower point, it gains speed, resulting in an increase in kinetic energy. At this point, all of the potential energy has been converted into kinetic energy, making it the maximum.
7.
The capacity to do work
Correct Answer
E. energy
Explanation
Energy is the correct answer because it is the capacity to do work. It encompasses various forms such as force, magnetism, kilowatts, and electricity. Energy is required to perform any kind of work and is fundamental to all physical processes.
8.
A force of 20 newtons
pushing an object 5 meters in the direction of the force. How much work is done?
Correct Answer
E. None of the above
9.
An example of Potential Energy would be
Correct Answer
B. A book resting on a table
Explanation
Potential energy is the energy possessed by an object due to its position or condition. In this case, a book resting on a table has potential energy because it is in a position where it can potentially fall or be moved. The potential energy is stored in the book and can be converted into kinetic energy if the book falls off the table. The other options, a moving car and a speeding bullet, involve kinetic energy rather than potential energy.
10.
An example of a system having both kinetic and potential energy would be
Correct Answer
C. An object in free fall
Explanation
An object in free fall would have both kinetic and potential energy. As the object falls, it gains kinetic energy due to its motion. At the same time, it also has potential energy due to its position above the ground. As the object falls closer to the ground, its potential energy decreases while its kinetic energy increases. Therefore, an object in free fall is an example of a system that has both kinetic and potential energy.
11.
What is the kinetic energy of an object moving at the speed of speed of light?
Correct Answer
D. None of the above
Explanation
The kinetic energy of an object moving at the speed of light cannot be determined using classical mechanics. According to Einstein's theory of relativity, as an object approaches the speed of light, its mass increases infinitely and would require an infinite amount of energy to accelerate it to that speed. Therefore, it is not possible for an object to have a finite kinetic energy at the speed of light. Thus, the correct answer is "none of the above".
12.
1 kg-m/sec/sec is equal to
Correct Answer
A. 1 Newton
Explanation
1 kg-m/sec/sec is equal to 1 Newton. This is because Newton is the unit of force in the International System of Units (SI). The unit of force is defined as the amount of force required to accelerate a mass of 1 kilogram by 1 meter per second squared. Therefore, 1 kg-m/sec/sec is equivalent to 1 Newton.
13.
What is the potential energy for a box weighing 100 newtons that is taken up to a height of 30 meters?
Correct Answer
B. 3000 j
Explanation
The potential energy of an object is given by the formula PE = mgh, where m is the mass of the object, g is the acceleration due to gravity, and h is the height. In this case, the weight of the box is given as 100 newtons, which is equal to its mass multiplied by the acceleration due to gravity. Since the mass is not given, we can assume it to be 10 kg (as weight = mass × acceleration due to gravity, and acceleration due to gravity is approximately 10 m/s^2). Therefore, the potential energy can be calculated as PE = (10 kg) × (10 m/s^2) × (30 m) = 3000 J.
14.
A crank with a rope,a wheel,and an object can lift the object with ease
Correct Answer
D. Pulley
Explanation
A pulley is a simple machine that consists of a wheel with a groove and a rope or cable running through it. By pulling on one end of the rope, the object attached to the other end can be lifted with ease. The pulley reduces the amount of force required to lift the object by distributing it over multiple ropes and wheels, making it an efficient and effective way to lift heavy objects.
15.
According to Einstein, one kilogram of matter would give _____ joules of energy
Correct Answer
C. 9.0 × 10^16 joules
16.
Calculate the power of a bike rider who is able to accelerate
from rest to a speed of 13.4 in just 9.5 sec. We will
assume that the biker is on level ground and that the combined weight of the
biker and bike is 83.8 kg.
Correct Answer
D. 794 W
Explanation
The power of the bike rider can be calculated using the formula: power = force × velocity. In this case, the force can be calculated using Newton's second law, which states that force = mass × acceleration. The acceleration can be calculated by dividing the change in velocity by the time taken. Using the given information, we can calculate the force, and then multiply it by the velocity to find the power. The correct answer of 794 W is obtained by performing these calculations correctly.
17.
Unit for momentum
Correct Answer
B. N m
Explanation
The unit for momentum is N m, which stands for Newton meter. Momentum is a vector quantity that represents the motion of an object and is defined as the product of its mass and velocity. The Newton (N) is the unit of force, and when multiplied by the meter (m), which is the unit of displacement, it gives the unit for momentum. Therefore, N m is the correct unit for momentum.
18.
Change in momentum
Correct Answer
D. Impulse
Explanation
Impulse is the correct answer because it is defined as the change in momentum of an object. When a force is applied to an object for a certain amount of time, it results in a change in momentum, which is known as impulse. Impulse is equal to the force applied multiplied by the time interval over which it acts. Therefore, impulse is the appropriate term to describe the change in momentum caused by a force.
19.
A truck is chasing a bicycle along a highway. Both have the same momentum. Which of the following is true?
Correct Answer
B. The bicycle will outrun the truck.
Explanation
The correct answer is "The bicycle will outrun the truck." This is because momentum is the product of mass and velocity, and since both the truck and bicycle have the same momentum, it means they must have different velocities. Since the bicycle has less mass than the truck, it must have a greater velocity in order to have the same momentum. Therefore, the bicycle will be able to outrun the truck.
20.
In a perfectly elastic collision
Correct Answer
A. No energy is lost in the system
Explanation
In a perfectly elastic collision, no energy is lost in the system. This means that the total kinetic energy before the collision is equal to the total kinetic energy after the collision. The objects involved in the collision exchange energy, but the total amount of energy in the system remains constant. This is because the collision is perfectly efficient, with no energy being converted into other forms such as heat or sound. Therefore, the statement "No energy is lost in the system" accurately describes a perfectly elastic collision.
21.
Two ice skaters colliding with each other but moving as one body after the collision is an example of
Correct Answer
C. A perfectly inelastic collision
Explanation
Two ice skaters colliding with each other and moving as one body after the collision is an example of a perfectly inelastic collision. In a perfectly inelastic collision, the two objects stick together and move as one object after the collision. This means that the kinetic energy is not conserved, as some of it is lost in the collision. However, the momentum is conserved, as the total momentum before the collision is equal to the total momentum after the collision.
22.
Two ice skaters, Daniel (mass 65.0 kg) and Rebecca (mass 45.0 kg), are
practicing. Daniel stops to tie his shoelace and, while at rest, is
struck by Rebecca, who is moving at 13.0 m/s before she collides with
him. After the collision, Rebecca has a velocity of magnitude 8.00 m/s
at an angle of 53.1 degrees from her initial direction. Both skaters
move on the frictionless, horizontal surface of the rink.What is the magnitude of Daniel's velocity after the collision?
Correct Answer
D. None of the above
Explanation
According to the law of conservation of momentum, the total momentum before the collision is equal to the total momentum after the collision. Since the skaters are on a frictionless surface, there is no external force acting on them. Therefore, the total momentum before the collision is equal to the total momentum after the collision.
Before the collision, the total momentum is given by the sum of the individual momenta of Daniel and Rebecca. After the collision, the total momentum is given by the sum of their individual momenta again.
Let's assume that the magnitude of Daniel's velocity after the collision is V. Since the collision is elastic, the magnitude of Rebecca's velocity after the collision will also be V.
Using the law of conservation of momentum, we can write the equation:
(mass of Daniel) * 0 + (mass of Rebecca) * 13.0 m/s = (mass of Daniel) * V + (mass of Rebecca) * V
Simplifying the equation, we get:
45.0 kg * 13.0 m/s = (65.0 kg + 45.0 kg) * V
585.0 kg m/s = 110.0 kg * V
V = 585.0 kg m/s / 110.0 kg
V ≈ 5.32 m/s
Therefore, the magnitude of Daniel's velocity after the collision is approximately 5.32 m/s.
23.
Less power is required while slowly lifting a box than while lifting it up quickly.
Correct Answer
A. True
Explanation
When lifting a box slowly, less power is required because the force applied is spread out over a longer period of time. This allows the person lifting the box to exert a smaller amount of force with each movement, making it easier to lift. On the other hand, when lifting a box quickly, more power is needed because the force applied must be greater to overcome the inertia and accelerate the box rapidly. Therefore, the statement that less power is required while slowly lifting a box is true.
24.
A simple machine may reduce the force required to do a task.
Correct Answer
A. True
Explanation
A simple machine is a device that can change the direction or magnitude of a force to make work easier. By using simple machines, such as levers, pulleys, or inclined planes, the force required to perform a task can be reduced. These machines allow us to apply a smaller force over a greater distance, which makes it easier to accomplish the task. Therefore, the statement that a simple machine may reduce the force required to do a task is true.
25.
The work required to lift a mass one meter depends on the speed at which it is raised.
Correct Answer
B. False
Explanation
The statement is false because the work required to lift a mass one meter does not depend on the speed at which it is raised. The work done is determined by the force exerted and the distance over which the force is applied. The amount of work done is the same regardless of the speed at which the mass is lifted.