1.
A roller coaster climbs up a hill at 4 m/s and then zips down the hill at 30 m/s. The momentum of the roller coaster
Correct Answer
B. Is greater coming down the hill
Explanation
The momentum of an object is given by its mass multiplied by its velocity. In this case, the roller coaster has a greater velocity (30 m/s) when it is going down the hill compared to when it is climbing up the hill (4 m/s). Since the mass of the roller coaster remains the same throughout the ride, the momentum is greater when it is coming down the hill.
2.
A soccer ball collides with another soccer ball at rest. The total momentum of the two soccer balls
Correct Answer
C. Remains the same
Explanation
When a soccer ball collides with another soccer ball at rest, the total momentum of the two soccer balls remains the same. This is because momentum is a conserved quantity, meaning it cannot be created or destroyed. In this case, the momentum of the first soccer ball before the collision is transferred to the second soccer ball, resulting in an equal and opposite momentum for the second ball. Therefore, the total momentum of the system (both soccer balls) remains constant.
3.
A swimmer with a mass of 75 kg dives off a boat with a mass of 500 kg. If the swimmer's speed is 4 m/s immediately after leaving the boat, what is the speed of the boat?
Correct Answer
C. 0.6 m/s
Explanation
When the swimmer dives off the boat, the total momentum before the dive is zero because the boat and the swimmer are initially at rest. According to the law of conservation of momentum, the total momentum after the dive should also be zero. Since the swimmer has a mass of 75 kg and a speed of 4 m/s, their momentum is 75 kg * 4 m/s = 300 kgÂ·m/s. To cancel out this momentum, the boat must have a momentum of -300 kgÂ·m/s. Since the boat has a mass of 500 kg, its speed can be calculated by dividing the momentum by the mass: -300 kgÂ·m/s / 500 kg = -0.6 m/s. Since the speed is a scalar quantity, the negative sign is ignored, giving a speed of 0.6 m/s. Therefore, the speed of the boat is 0.6 m/s.
4.
A 75 kg football player runs directly into an 80 kg football player running in the opposite direction. The momentum of the 80 kg football player after the collision will
Correct Answer
B. Decrease
Explanation
The momentum of an object is determined by its mass and velocity. In this scenario, the 75 kg football player is running directly into the 80 kg football player, meaning they have opposite velocities. When they collide, their momenta will cancel each other out to some extent, resulting in a decrease in the momentum of the 80 kg football player.
5.
A cannon fires a cannonball. The speed of the cannonball will be the same as the speed of the recoiling cannon
Correct Answer
A. If the mass of the cannonball equals the mass of the cannon
Explanation
The speed of the cannonball will be the same as the speed of the recoiling cannon if the mass of the cannonball equals the mass of the cannon because momentum is conserved. According to the law of conservation of momentum, the total momentum of an isolated system remains constant before and after an event. In this case, when the cannonball is fired, it gains momentum in one direction, and the cannon gains an equal amount of momentum in the opposite direction to conserve the overall momentum of the system. Since the masses of the cannonball and the cannon are equal, their velocities will also be equal to maintain momentum conservation.
6.
A 2kg ball has a momentum of 30 kgm/s. What is the ball's speed?
Correct Answer
B. 15 m/s
Explanation
The momentum of an object is calculated by multiplying its mass by its velocity. In this question, we are given the momentum of a 2kg ball, which is 30 kgm/s. To find the ball's speed, we need to divide the momentum by the mass. Therefore, 30 kgm/s divided by 2kg gives us a speed of 15 m/s.
7.
A 20 kg shopping cart moving at a velocity of 0.5 m/s collides into a store wall and stops. The momentum of the shopping cart after the crash
Correct Answer
B. Decreases
Explanation
The momentum of an object is defined as the product of its mass and velocity. In this scenario, the shopping cart has a mass of 20 kg and a velocity of 0.5 m/s. When it collides into the store wall and stops, its velocity becomes zero. As a result, the momentum of the shopping cart decreases because the velocity component in the momentum equation is reduced to zero. Therefore, the correct answer is "decreases".
8.
A moving freight car runs into an identical car at rest on the track. If the two freight cars join together, their velocity will be
Correct Answer
B. Half as much as the freight car before the collision
Explanation
When the moving freight car collides with the identical car at rest, the two cars join together and form a single object. 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 second car was at rest, its momentum is zero. Therefore, the momentum of the combined object after the collision is equal to the momentum of the moving freight car before the collision. Since momentum is directly proportional to velocity, the velocity of the combined object will be half as much as the velocity of the moving freight car before the collision.
9.
Which of the following has the largest momentum?
Correct Answer
C. A pickup truck traveling down the highway
Explanation
The momentum of an object is directly proportional to its mass and velocity. In this case, the pickup truck traveling down the highway would have the largest momentum because it has both a significant mass and is moving with a certain velocity. The truck parked in a parking lot and the school building have zero velocity, so their momentum would be zero. The dog chasing a truck down the street may have some velocity, but its mass would be much smaller compared to the pickup truck, resulting in a smaller momentum.
10.
A 5 kg chunk of clay is thrown at a stationary 7 kg bowling ball. The clay sticks to the bowling ball, and the objects are set in motion. If the initial velocity of the clay before it hit the bowling ball was 10 m/s. The momentum of the bowling ball + stuck on clay is
Correct Answer
D. 50 kgm/s
Explanation
When the clay sticks to the bowling ball, they become a single object with a combined mass of 12 kg (5 kg + 7 kg). According to the law of conservation of momentum, the total momentum before and after the collision must be the same. Since the clay was initially in motion, it had momentum, and this momentum is transferred to the bowling ball when they stick together. Therefore, the momentum of the bowling ball + stuck on clay is 50 kgm/s.