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22 Cards in this Set
- Front
- Back
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How does impulse differ from force! |
Impulse- a force that produces motion suddenly |
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2 ways to increase impulse |
-increase the force
- increase the time interval |
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For the same force, why does a long cannon impart more speed to a cannonball than a smaller cannon?
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It will have more momentum coming from the long cannon due to the force acting for more time
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Is the impulse-momentum relationship related to Newton's second law?
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It is a direct result; Impulse= Change in the Momentum |
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To impart the greatest momentum to an object, should you exert the largest force possible, extend that force for as long a time as possible, or both? Explain. |
Both, for then the quantity Ft is greater.
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When you are in the way of a moving object and an impact force is your fate, are you better off decreasing its momentum over a short time or over a long time? Explain.
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The force of impact will be less if momentum changes over a long time. By making time long, F will be smaller. |
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Which undergoes the greatest change in momentum: (1) a baseball that is caught, (2) a baseball that is thrown, or (3) a baseball that is caught and then thrown back, if the baseballs have the same speed just before being caught and just after being thrown?
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(3) There is twice the momentum change for the baseball that is caught and then thrown back. A change in stopping, and the same change in returning.
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In the preceding question, in which case is the greatest impulse required?
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Greatest impulse also for (3) because of the greater change in momentum. |
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Can you produce a net impulse on an automobile by sitting inside and pushing on the dashboard? Can the internal forces within a soccer ball produce an impulse on the soccer ball that will change its momentum?
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No for both, for the forces, and hence impulses, are internal.
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Is it correct to say that if no net impulse is exerted on a system, then no change in the momentum of the system will occur?
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Correct |
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What does it mean to say that momentum (or any quantity) is conserved?
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It means that in any interaction where external impulses don’t occur, the momentum of a system remains the same before and after the interaction. In general it means that the magnitude of the quantity remains unchanged while other changes may take place.
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When a cannonball is fired, momentum is conserved for the system of cannon + cannonball. Would momentum be conserved for the system if momentum were not a vector quality? Explain.
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No, the momentum would not be conserved if momentum were not a vector quantity because then it would not cancel. That is, the momentum of the cannon + the momentum of the cannonball would be twice the momentum of the cannon and it would have increased from zero. |
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Distinguish between an elastic collision and an inelastic collision. For which type of collision is momentum conserved?
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An elastic collision is one where rebound is without lasting deformation or the generation of heat. An inelastic collision is one where deformation does occur, or heat is generated. Momentum is conserved for both types. |
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Railroad car A rolls at a certain speed and makes a perfectly elastic collision with car B of the same mass. After the collision, car A is observed to be at rest. How does the speed of car B compare with the initial speed of car A? |
Momentum is completely transferred from car A to car B. Since the masses are the same, the speed of Car B is equal to the initial speed of car A.
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If the equally massive cars of the previous question stick together after colliding inelastically, how does their speed after the collision compare with the initial speed of car A?
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Again, the momentum of car A is transferred, this time to both cars. Since twice the mass is moving after collision, the speed is half.
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What is the momentum of a 50-kg carton that slides at 4 m/s across an icy surface?
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momentum = mass * velocity; momentum = 50 * 4; momentum = 200 kg m/s |
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What impulse occurs when an average force of 10 N is exerted on a cart for 2.5 s? |
Average force is(F) =10N; Time taken by the cart to exert is(t) =2.5s |
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What is the impulse of an 8kg ball rolling at 2m/s when it bumps into a pillow and stops?
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Mass of the ball is(Δm) =8kg; Speed of the ball(v) = 2m/s |
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A 2kg blob of putty moving at 3m\s slams into a 2kg blob at rest. Calculate the speed of the two stuck together?
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2 kg X 3 m/s + 2 kg X 0= 4kg X v
→ V= 3/2 m/s = 1.5 m/s |
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A car crashes into a wall at 25 m s and is brought to rest in 0.1 s. calculate the average force exerted on a 75 kg test dummy by the seat belt. |
impulse= 25 m/s X 75 kg; 1,875 kg X m/s
Force X time= 1,875 kg X m/s Force= 1,875 kg/ 0.1 s Force= 18,750 N |
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A 5-kg fish swimming 1 m/s swallows an absent-minded 1-kg fish swimming toward it at a velocity that brings fish to a halt immediately after lunch. What is velocity of the smaller fish before lunch?
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M = mass of the larger fish; V = velocity of the larger fish
m = mass of the smaller fish; v = velocity of the smaller fish (5 kg)(1 m/s) = (1 kg)(x m/s); = 5 m/s |
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Two automobiles, each of mass 1000 kg, are moving at the same speed, 20 m/s, when they collide and stick together. In what direction and at what speed does the wreckage move a) if one car was driving north and one south? b) if one car was driving north and one east?
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-Since m1 = m2 = 1000kg, v1 going n with (+20m/s in +y), v2 going s (-20m/s in-y)
Initial momentum is m1v1 + m2v2 = 1000x20 + 1000x(-20) = 0 - Speed and direction of the cars after collision is 20 root 2 in north east direction. |
