Which situation best represents a closed environment?
two balls colliding in deep space
two balls colliding on a pool table
two balls colliding in midair
two balls colliding under water
Correct answer is deep space
Conservation of Momentum Unit Test (ESSAY ANSWERS) (! DO NOT COPY AND PASTE OR THEY WILL KNOW THAT YOU CHEATED !)
15. A hockey puck with a mass of 0.16 kg travels at a velocity of 40 m/s toward a goalkeeper. The goalkeeper has a mass of 120 kg and is at rest. Assuming a closed system, find the total momentum of the goalkeeper and puck after the puck is caught by the goalkeeper. In 3-4 sentences, identify the object with the greater momentum after the puck is caught and explain your reasoning.
The goalkeeper has more momentum than the puck after the puck is caught, since the goalkeeper has more mass.
P mv.......P (before) = P (after)
Puck m1 = 0.16 kg
Puck v1 = 40 m/s 0.16 kg x 40 m/s = 6.4 kg m/s
Goalkeeper m2 = 120 kg 120 kg x 0 m/s = 0 kg m/s
Goalkeeper v2 = 0 m/s
6.4kg m/s + 0 kg m/s = P ( 6.4 kg m/s = P)
16. Why is Newton’s cradle (Newton’s balls) described as an “almost-ideal” closed system? Explain your reasoning in one or two sentences.
Newton's cradle is an almost-ideal closed system because it eventually comes to a stop due to external forces. Air resistance slows the balls down, making them gradually stop going back and forth.
17.A blue and a green billiard ball, each with a mass of 0.15 kg, collide directly. Before the collision, the blue ball had a speed of 3 m/s while the green ball had a speed of 2 m/s. After the collision, the blue ball stays in place while the green ball continues in motion.
In 3-4 sentences, represent the situation before and after the collision and calculate the speed of the green ball after the collision. Be sure to discuss direction.
Before the collision, the green ball is moving at 2 m/s towards the blue ball moving at 3 m/s, each weigh 15kg. After the collision, the blue ball stops, and the green ball keeps moving in the opposite direction.
The negative direction would be left, while the positive direction would be right.
(M1 v 1 + m 2 v 2 = p) (0.15kg) (2 m/s)
+ (0.15kg) (-3 m/s) = p
0.3kg.m/s + -.45kg.m/s = p
-0.15kg.m/s = p
The green ball's mass is 0.15 kg, so the ball would move backwards at a momentum of -0.15 kg.m/s making the velocity of the green ball -0.15 m/s / 0.15 kg. Meaning that the velocity of the green ball is -1 m/s.
18. Suppose that a cart is moving along a road at a constant velocity. Give two examples of ways to cause the cart to decelerate, explaining how the net force is affected.
One example of the way that you can make the cart decelerate, is putting down your foot to slow the cart or bring it to a stop. This will increase the net force. A second example is possibly riding it somewhere with high air resistance. This will also increase net force.
19. Using two billiard balls, in 3-4 sentences, design an experiment to demonstrate the law of conservation of momentum.
If the two balls are the same weight with the same velocity and acceleration, after the collision, their momentum should still be the same. For an example,: One ball that is 10 kg with a velocity of 6 m/s, collides with another ball with the same kg and velocity, both balls should either move in the same direction or stop.
Conservation of Momentum Unit Test answers:
-What is the momentum of a car with a mass of 2,000 kg moving at a constant velocity of 20 m/s?
40,000 kg⋅m/s
-A large metal ball is at rest, and a small rubber ball is moving at a high velocity. When they collide, the large metal ball begins to roll slowly. What must have happened to the momentum of the small rubber ball?
It must have decreased.
-If an astronaut in space pushes off the satellite she is working on, what will happen to her if there are no other acting external forces?
She will move in the same direction at the same speed forever.
-Which situation best represents a closed environment?
two balls colliding in deep space
-Which force, in real life, will have the least effect on a bowling ball rolling down a lane toward bowling pins?
magnetism
-A boxer throws a punch with a force of 1,400 N that lasts 0.02 s. What is the impulse of this punch?
28 kg⋅m/s
-A small ball with a mass of 0.6 kg and a velocity of 12 m/s hits another ball with the same mass. The first ball stops moving, and the second ball then moves forward and hits a third ball with a mass of 0.2 kg. If the system is closed, what is the velocity of the third ball?
36 m/s
-The total momentum of a system of two moving identical bodies is zero.
What should be true about the velocities of the bodies?
The velocities should be equal in magnitude and opposite in direction.
-A car with a mass of 1,250 kg travels at 2.24 m/s and bumps into a stopped car with a mass of 1,300 kg. After the collision, the two cars stick together and move forward. How fast will they both move forward? Round your answer to two decimal places.
1.10 m/s
-Which formula for net force contains an error?
Fnet=Δv/Δt (Or B)
-If the net force of a system is a non-zero constant and the mass decreases, what must be true about the acceleration?
The acceleration increases.
-If an object is moving at a constant velocity, which must be true?
Its acceleration is zero.
-Which series of steps describes how to demonstrate conservation of momentum in a system of two moving particles that collide?
Determine the momentums of the two particles before the collision and add them together. Determine the momentums of the two particles after the collision and add them together. Verify that both sums are the same.
-Two ice skaters want to prove conservation of momentum. Skater A has a mass of 72 kg, and skater B has a mass of 48 kg. They are originally at rest. They hold hands and face each other. They then push off each other and move in opposite directions. Skater B moves with a velocity of 3 m/s.
What must the velocity of skater A be in the opposite direction after the push in order to prove conservation of momentum?
2.0 m/s
(The rest are essay questions, I will type my answer, but make sure to re-word it VERY differently)
Conservation of Momentum Unit Test answers:
(For people who don't want to read: Simplified)
1. 40,000 kg⋅m/s
2. It must have decreased.
3. She will move in the same direction at the same speed forever.
4. two balls colliding in deep space
5. magnetism
6. 28 kg⋅m/s
7. 36 m/s
8. The velocities should be equal in magnitude and opposite in direction
9. 1.10 m/s
10. Fnet=Δv/Δt (Or C! I made a mistake in the other version!)
11. The acceleration increases.
12. Its acceleration is zero.
13. Determine the momentums of the two particles before the collision and add them together. Determine the momentums of the two particles after the collision and add them together. Verify that both sums are the same.
14. 2.0 m/s
Which formula for net force contains an error?
Fnet=triangle v over triangle t
On mine it is A
1. 40,000 kg⋅m/s
2. It must have decreased.
3. She will move in the same direction at the same speed forever.
4. two balls colliding in deep space
5. magnetism
6. 28 kg⋅m/s
7. 36 m/s
8. The velocities should be equal in magnitude and opposite in direction
9. 1.10 m/s
10. Fnet=Δv/Δt (Or C! I made a mistake in the other version!)
11. The acceleration increases.
12. Its acceleration is zero.
Essay quistions are changed