PY 205 C3H3:

1)

A moving electron passes near the nucleus of a gold atom, which contains 79 protons and 118 neutrons. At a particular moment the electron is a distance of 4.0 x 10-9 m from the gold nucleus. (a) What is the magnitude of the electric force exerted by the gold nucleus on the electron? IF on electron = N (b) What is the magnitude of the electric force exerted by the electron on the gold nucleus? IF `on gold nucleus =55141 e ,/ a / zero nagnliude The diagram above shows two positively charged objects and one negatively charged object. The absolute value of the charge on each object is the same. Which arrow (a-j) best represents the direction of the net electric force on the negatively charged object? -Select- V Select a J 10"\\l/I r) 63 r) 971:, 5 I zero mangude The diagram above shows two negatively charged objects and one positively charged object. The absolute value of the charge on each object is the same. Which arrow (a-j) best represents the "51' ' ,gfnt e_net electric force on the positively charged object? (a) Two thin hollow plastic spheres, about the size of a ping-pong ball with masses (m, = my = 2e-3 kg) have been rubbed with wool. Sphere 1 has a charge q1 = -5e-9 C and is at location m. Sphere 2 has a charge 92 = -5e-9 C and is at location m. It will be useful to draw a diagram of the situation, including the relevant vectors. What is the relative position vector pointing from q1 to qz? F = m What is the distance between q1 and q2? 171 = m What is the unit vector * in the direction of ? r = What is the magnitude of the gravitational force exerted on q2 by q1? I Fgrav on q21 = What is the gravitational force (vector) exerted on q2 by q1? Fgrav on 92 = N 1 9192 What is the value of 47 co (F| ? What is the electric force (vector) exerted on q2 by q1? Felectric on 92 = (b) What is the ratio of the magnitude of the electric force to the magnitude of the gravitational force? Felectric Fgrau (You see that electric forces between two small charged objects are typically very much larger than gravitational forces between those same small objects. It takes the entire mass of the Earth to exert a sizable gravitational force on a small object.) (c) If the two masses were 3 times farther away (that is, if the distance between the masses were 3x | | ), what would be the ratio of the magnitude of the electric force to the magnitude of the gravitational force now? Felectric FgravThe windshield of a speeding car hits a hovering insect. Consider the time interval from just before the car hits the insect to just after the impact. For which choice of system is the change of momentum zero? The system consisting of the car alone. The system consisting of the bug plus the car. The system consisting of the bug alone. Compare the magnitude of the change of momentum of the bug to that of the car: The magnitudes of the change of momentum are equal. The magnitude of change of momentum of the bug is bigger. The magnitude of change of momentum of the car is bigger. Compare the magnitude of the change of velocity of the bug to that of the car: The magnitude of change of velocity of the bug is bigger. The magnitude of change of velocity of the car is bigger. The magnitudes of the change of velocity are equal. You and a friend each hold a lump of wet clay. Each lump has a mass of 35 grams. You each toss your lump of clay into the air, where the lumps collide and stick together. Just before the impact, the velocity of one lump was m/s, and the velocity of the other lump was m/s. What was the the total momentum of the lumps just before the impact? _. Ptotal = kg ' m/S- What is the momentum of the stuck-together lump just after the collision? 3: kg - m/s. What is the velocity of the stuck-together lump just after the collision? * v; = m/s. Consider the head-on collision of two identical bowling balls, each with mass 7 kg (see gure). Ball A with velocity V = m/s strikes ball Bl which was at rest Then ball A stops and ball B moves with the same velocity 7 that ball A had initially. M M ' a J J Initially aI resl Initial slaie (before collision) Final state (after collision) M M A B' a J New at rest (3) Choose a system consisting only of ball A. What is the momentum change of the system during the collision? Asyscem = kg - m/s What is the momentum change of the surroundings? ABsurroundings = kg ' m/s (b) Choose a system consisting only of ball 5. What is the momentum change of the system during the collision? Asyszem = k9 - m/s What is the momentum change of the surroundings? Asurroundings = kg - m/s (c) Choose a system consisting of both ballsl What is the momentum change of the system during the collision? Asyscem = kg ~ m/s What is the momentum change of the surroundings? ABsurroundings = kg ~ m/s A bullet of mass 0.111 kg traveling horizontally at a speed of 300 m/s embeds itself in a block of mass 2 kg that is sitting at rest on a nearly frictionless surface. What is the speed of the block after the bullet embeds itself in the block? v = m/s A car of mass 2600 kg collides with a truck of mass 4700 kg, and just after the collision the car and truck slide along, stuck together: The car's velocity just before the collision was m/s, and the truck's velocity just before the collision was m/s. (a) What is the velocity of the stuck-together car and truck just after the collision? m/s (b) In your analysis in part (a), why can you neglect the effect of the force of the road on the car and truck? Short collision time, negligible impulse compared to large impulse acting between car and truck. The road doesn't exert forces on the car or truck and doesn't affect the vehicles. Object A has mass mA = 9 kg and initial momentum 17A], = kg ~ m/s, just before it strikes object B, which has mass m5 = 11 kg. Just before the collision object B has initial momentum FAB], = kg ' m/s. Consider a system consisting of both objects A and B. What is the total initial momentum of this system, just before the collision? 1'5st = kg - m/s The forces that A and B exert on each other are very large but last for a very short time If we choose a time interval from just before to just after the collision, what is the approximate value of the impulse applied to the two-object system due to forces exerted on the system by objects outside the system? FmAt = N - s Therefore, what does the Momentum Principle predict that the total nal momentum of the system will be, just after the collision? st= k9 - "1/5 Just after the collision, object A is observed to have momentum FA], = kg - m/st What is the momentum of object B just after the collision? F5; = kg - m/s