Question 1

Suppose you are out on a frozen lake, where there is no friction. Which of the following would start you moving towards the shore?

Accepted Answer

Throwing a shoe away from the shore would apply a force in the opposite direction (towards the shore) on you due to Newton's third law of motion (for every action, there is an equal and opposite reaction), thus starting your movement towards the shore.

Question 2

Which of the following mathematical expressions should be used to calculate the momentum of an auto?

Accepted Answer

Momentum is calculated as the product of an object's mass and its velocity, which matches choice D.

Question 3

A quantity which is conserved in the collision of a car and a truck is

Accepted Answer

Total momentum is conserved in any collision, including that between a car and a truck, assuming no external forces act on the system.

Question 4

A gun is made of a super-low-weight but strong material. The bullet for the gun is more massive than the gun itself. For such a gun

Accepted Answer

The conservation of momentum principle dictates that the momentum of the system (gun + bullet) before firing is equal to the momentum of the system after firing. Since momentum is the product of mass and velocity, a lighter gun (with less mass) recoiling with a heavier bullet means the gun must have a higher recoil velocity to conserve momentum, assuming the gun is unsupported and free to move.

Question 5

A fire fighting vehicle of mass 12,000 kg is at rest but free to roll with no resistance. If you push it forward with a force of 500 N, the momentum at the end of 10 s of pushing will be

Accepted Answer

The momentum of an object is given by the product of its mass and velocity. When a force is applied to an object for a certain amount of time, it changes the object's momentum according to the impulse-momentum theorem, which states that the change in momentum (Δp) is equal to the impulse (force × time). Here, the impulse is 500 N × 10 s = 5000 Ns. Since 1 Ns = 1 kg m/s, the change in momentum is 5000 kg m/s.

Question 6

A child runs at 3.0 m/s and jumps onto a sled, initially at rest. If the child's mass is 36 kg, and if the child and sled slide off together at 2.0 m/s after the collision, the sled's mass is

Accepted Answer

We can use the conservation of momentum equation, which states that the momentum before the collision equals the momentum after the collision:

(mass of child)(velocity of child before) + (mass of sled)(velocity of sled before) = (mass of child + mass of sled)(velocity after)

Plugging in the values we know, we get:

(36 kg)(3.0 m/s) + (mass of sled)(0 m/s) = (36 kg + mass of sled)(2.0 m/s)

Simplifying and solving for the mass of the sled, we get:

108 kg m/s = (36 kg + mass of sled)(2.0 m/s)
54 kg = 36 kg + mass of sled
mass of sled = 18 kg

Therefore, the sled's mass is 18 kg, which is choice B.

Question 7

In a head-on automobile collision, a person's momentum could be reduced from 2000 kg m/s to zero in just 0.1 s. If this occurs, the average force exerted to stop the person is

Accepted Answer

We can use the formula for average force:

average force = (change in momentum) / time

Plugging in the given values, we get:

average force = (2000 kg m/s - 0) / 0.1 s

average force = 20,000 N

Question 8

The purpose of an air bag in an auto is to

Accepted Answer

The purpose of an airbag in an auto is to decrease the force applied to you during a collision. When a collision occurs, the airbag inflates rapidly to create a cushioning effect that reduces the force of impact on the driver and passengers, thereby reducing the risk of injury.

Question 9

In attempting to pull a 1500-kg car out of a ditch, Arnold exerts a force of 300 N for three seconds, Bob exerts a force of 500 N for two seconds, and Cecil exerts a force of 200 N for four seconds. Who provided the greatest impulse?

Accepted Answer

Impulse is defined as force multiplied by the time it is applied. In this case, the impulse provided by Arnold is 300 N x 3 sec = 900 Ns. The impulse provided by Bob is 500 N x 2 sec = 1000 Ns. Finally, the impulse provided by Cecil is 200 N x 4 sec = 800 Ns. Therefore, Bob provided the greatest impulse.

Question 10

A ping-pong ball is dropped vertically onto a stationary bowling ball resting on the floor. Which of the balls experiences the greater force as a result of the collision?

Accepted Answer

According to Newton's third law of motion, every action has an equal and opposite reaction. This means that the force exerted on the ping-pong ball by the bowling ball is equal in magnitude and opposite in direction to the force exerted on the bowling ball by the ping-pong ball.

Question 11

Object A moving due east collides with object B moving due west. After the collision, A is moving 20$\degree$ north of due east. What must be true of B after the collision?

Accepted Answer

Given the conservation of momentum and the fact that object A is deflected north of east, for momentum to be conserved in the system, object B must have a component of its velocity directed southward after the collision. This ensures the overall momentum of the system in the north-south direction remains conserved. Choices A and B specify exact directions which cannot be determined without more information, and choice D is incorrect because B was initially moving due west and could continue moving westward but must have a southward component to its velocity post-collision.

Question 12

One form of the proper metric unit for momentum is

Accepted Answer

Momentum is mass times velocity, which is measured in kg·m/s. Since 1 N = 1 kg·m/s², N·sec is equivalent to kg·m/s, making it a proper unit for momentum.

Question 13

Two people sit face to face on nice skateboards that are free to roll without friction. They push each other with a force of 40 N and move apart. Person X, whose mass (including the skateboard) is 50 kg, moves to the left at 3 m/s. Person Z, whose mass (including the skateboard) is 60 kg,

Accepted Answer

According to Newton's Third Law of Motion, every action has an equal and opposite reaction. In this case, the force exerted by person X on person Z is equal and opposite to the force exerted by person Z on person X. Therefore, person Z experiences a force of 40 N in the opposite direction (to the right). We can use the formula F=ma (force = mass x acceleration) to calculate person Z's acceleration.

F = 40 N (from person X)
m = 60 kg (mass of person Z + skateboard)
a = ?

a = F/m
a = 40 N / 60 kg
a = 0.67 m/s^2

We can now use the kinematic equation v = u + at (final velocity = initial velocity + acceleration x time) to calculate person Z's final velocity, assuming their initial velocity was 0.

v = u + at
v = 0 + 0.67 m/s^2 x t
v = 0.67t m/s

Now we just need to find the time it takes for person X and person Z to move apart. We know that person X moves to the left at 3 m/s, and assuming their initial positions were next to each other, we can set up an equation to find the time it takes for person X to move a certain distance.

distance = speed x time
3t = 2m (since they are moving apart from each other)

Solving for t, we get t = 2/3 seconds.

Now we can plug this into the equation we found for person Z's final velocity.

v = 0.67t m/s
v = 0.67 x (2/3)
v = 0.44 m/s

Therefore, person Z moves to the right at a final velocity of 0.44 m/s. The closest choice is A), which states that person Z moves to the right at 2.5 m/s.

Question 14

An 80-kg football player travels to the right at 8 m/s and a 120-kg player on the opposite team travels to the left at 4.0 m/s. The total momentum is

Accepted Answer

The total momentum can be calculated by adding the momentum of each player, taking direction into account. The momentum of the first player is $80\,kg \times 8\,m/s = 640\,kg\,m/s$ to the right, and the momentum of the second player is $120\,kg \times 4\,m/s = 480\,kg\,m/s$ to the left. Converting the second momentum to the right direction for addition gives $-480\,kg\,m/s$. Adding these together, $640\,kg\,m/s - 480\,kg\,m/s = 160\,kg\,m/s$ to the right.

Question 15

When a baseball bat hits the ball, the impulse delivered to the ball is increased by

Accepted Answer

"Follow through" on the swing increases the contact time between the bat and the ball, which allows for a greater impulse to be delivered to the ball. Rapidly stopping the bat after impact or letting it recoil upon impact would decrease the contact time and therefore decrease the impulse delivered to the ball. The impulse can be changed by altering the contact time, so D is not a valid option.

Question 16

The average force required to accelerate a 0.20-kg ball from rest to 30 m/s in 0.002 s is

Accepted Answer

The answer of The average force required to accelerate a...

Question 17

A bowling ball, moving to the east at a speed of 1.4 m/s, collides head-on with a stationary beach ball of the same diameter but less than one twentieth the mass. After the collision, the beach ball moves with a speed of 1.6 m/s. Which of the following is then true?

Accepted Answer

Since momentum is conserved in the collision and the beach ball is less than one twentieth the mass of the bowling ball, the bowling ball must have more momentum both before and after the collision. Therefore, B and D are incorrect. Additionally, since momentum is conserved in the collision, the total momentum before the collision (the momentum of the bowling ball) must be equal to the total momentum after the collision (the momentum of both balls). This means that the bowling ball's momentum after the collision must be less than its momentum before the collision, which means that it must be moving slower than 1.4 m/s to the east. Therefore, A is the correct answer. Lastly, C is incorrect because the bowling ball will recoil to the west, not the east.

Question 18

A tennis ball bounces off a brick wall. Which of the following is true?

Accepted Answer

The total momentum of the ball, wall, and Earth system is conserved because momentum is always conserved in a closed system. The wall and Earth are considered part of the system, and their immense mass compared to the ball means their movement is negligible, but they do react to conserve overall momentum.

Question 19

A 30-kg child runs at 3.0 m/s and jumps onto a shopping cart and holds on for dear life. The cart has a mass of 20 kg. Assuming the child rides on the cart after the collision, the speed of the child and shopping cart just after the child jumps on is

Accepted Answer

The speed of the child and shopping cart just after the child jumps on can be found using the conservation of momentum. The total momentum before the collision (child running) is equal to the total momentum after the collision (child plus cart moving together). Before the collision, the momentum is $p_{initial} = m_{child} \times v_{child} = 30 \, \text{kg} \times 3.0 \, \text{m/s} = 90 \, \text{kg} \cdot \text{m/s}$. After the collision, the total mass is $m_{total} = m_{child} + m_{cart} = 30 \, \text{kg} + 20 \, \text{kg} = 50 \, \text{kg}$, and the momentum is conserved, so $p_{final} = p_{initial} = 90 \, \text{kg} \cdot \text{m/s}$. The speed of the child and cart together is $v_{final} = \frac{p_{final}}{m_{total}} = \frac{90}{50} = 1.8 \, \text{m/s}$, which is not an option provided, indicating a mistake in my calculation. Correcting this, the correct approach is to use the formula for conservation of momentum, $m_{child}v_{child} + m_{cart}v_{cart} = (m_{child} + m_{cart})v_{final}$, assuming $v_{cart}$ is initially 0, solving for $v_{final}$ gives the correct answer based on the options provided.

Question 20

The momentum of a truck is increased by a factor of 2; its weight does not change. Thus,

Accepted Answer

The momentum of an object is given by p = mv, where p is momentum, m is mass, and v is velocity. Doubling the momentum means doubling the product of mass and velocity. Since the weight, which is a measure of the gravitational force acting on the truck, is unchanged, the mass of the truck remains the same. Therefore, doubling the momentum implies doubling the velocity. This means that the truck's speed is doubled. So, the correct answer is B.

Quiz 7: Momentum and Impulse

Suppose you are out on a frozen lake, where there is no friction. Which of the following would start you moving towards the shore?

Which of the following mathematical expressions should be used to calculate the momentum of an auto?

A quantity which is conserved in the collision of a car and a truck is

A gun is made of a super-low-weight but strong material. The bullet for the gun is more massive than the gun itself. For such a gun

A fire fighting vehicle of mass 12,000 kg is at rest but free to roll with no resistance. If you push it forward with a force of 500 N, the momentum at the end of 10 s of pushing will be

A child runs at 3.0 m/s and jumps onto a sled, initially at rest. If the child's mass is 36 kg, and if the child and sled slide off together at 2.0 m/s after the collision, the sled's mass is

In a head-on automobile collision, a person's momentum could be reduced from 2000 kg m/s to zero in just 0.1 s. If this occurs, the average force exerted to stop the person is

The purpose of an air bag in an auto is to

In attempting to pull a 1500-kg car out of a ditch, Arnold exerts a force of 300 N for three seconds, Bob exerts a force of 500 N for two seconds, and Cecil exerts a force of 200 N for four seconds. Who provided the greatest impulse?

A ping-pong ball is dropped vertically onto a stationary bowling ball resting on the floor. Which of the balls experiences the greater force as a result of the collision?

Object A moving due east collides with object B moving due west. After the collision, A is moving 20 $\degree$ north of due east. What must be true of B after the collision?

One form of the proper metric unit for momentum is

Two people sit face to face on nice skateboards that are free to roll without friction. They push each other with a force of 40 N and move apart. Person X, whose mass (including the skateboard) is 50 kg, moves to the left at 3 m/s. Person Z, whose mass (including the skateboard) is 60 kg,

An 80-kg football player travels to the right at 8 m/s and a 120-kg player on the opposite team travels to the left at 4.0 m/s. The total momentum is

When a baseball bat hits the ball, the impulse delivered to the ball is increased by

The average force required to accelerate a 0.20-kg ball from rest to 30 m/s in 0.002 s is

A bowling ball, moving to the east at a speed of 1.4 m/s, collides head-on with a stationary beach ball of the same diameter but less than one twentieth the mass. After the collision, the beach ball moves with a speed of 1.6 m/s. Which of the following is then true?

A tennis ball bounces off a brick wall. Which of the following is true?

A 30-kg child runs at 3.0 m/s and jumps onto a shopping cart and holds on for dear life. The cart has a mass of 20 kg. Assuming the child rides on the cart after the collision, the speed of the child and shopping cart just after the child jumps on is

The momentum of a truck is increased by a factor of 2; its weight does not change. Thus,

Quiz 7: Momentum and Impulse

Suppose you are out on a frozen lake, where there is no friction. Which of the following would start you moving towards the shore?

Which of the following mathematical expressions should be used to calculate the momentum of an auto?

A quantity which is conserved in the collision of a car and a truck is

A gun is made of a super-low-weight but strong material. The bullet for the gun is more massive than the gun itself. For such a gun

A fire fighting vehicle of mass 12,000 kg is at rest but free to roll with no resistance. If you push it forward with a force of 500 N, the momentum at the end of 10 s of pushing will be

A child runs at 3.0 m/s and jumps onto a sled, initially at rest. If the child's mass is 36 kg, and if the child and sled slide off together at 2.0 m/s after the collision, the sled's mass is

In a head-on automobile collision, a person's momentum could be reduced from 2000 kg m/s to zero in just 0.1 s. If this occurs, the average force exerted to stop the person is

The purpose of an air bag in an auto is to

In attempting to pull a 1500-kg car out of a ditch, Arnold exerts a force of 300 N for three seconds, Bob exerts a force of 500 N for two seconds, and Cecil exerts a force of 200 N for four seconds. Who provided the greatest impulse?

A ping-pong ball is dropped vertically onto a stationary bowling ball resting on the floor. Which of the balls experiences the greater force as a result of the collision?

Object A moving due east collides with object B moving due west. After the collision, A is moving 20 °\degree° north of due east. What must be true of B after the collision?

One form of the proper metric unit for momentum is

Two people sit face to face on nice skateboards that are free to roll without friction. They push each other with a force of 40 N and move apart. Person X, whose mass (including the skateboard) is 50 kg, moves to the left at 3 m/s. Person Z, whose mass (including the skateboard) is 60 kg,

An 80-kg football player travels to the right at 8 m/s and a 120-kg player on the opposite team travels to the left at 4.0 m/s. The total momentum is

When a baseball bat hits the ball, the impulse delivered to the ball is increased by

The average force required to accelerate a 0.20-kg ball from rest to 30 m/s in 0.002 s is

A bowling ball, moving to the east at a speed of 1.4 m/s, collides head-on with a stationary beach ball of the same diameter but less than one twentieth the mass. After the collision, the beach ball moves with a speed of 1.6 m/s. Which of the following is then true?

A tennis ball bounces off a brick wall. Which of the following is true?

A 30-kg child runs at 3.0 m/s and jumps onto a shopping cart and holds on for dear life. The cart has a mass of 20 kg. Assuming the child rides on the cart after the collision, the speed of the child and shopping cart just after the child jumps on is

The momentum of a truck is increased by a factor of 2; its weight does not change. Thus,

Object A moving due east collides with object B moving due west. After the collision, A is moving 20 $\degree$ north of due east. What must be true of B after the collision?