I use a rope 2.00 m long to swing a 10.0-kg weight around my head. The tension in the rope is 20.0 N. In half a revolution how much work is done by the rope on the weight? d. 0 (tension perpendicular to velocity) The work done by static friction can be: d. Any of the above. (surface exerting friction can move) A satellite is held in orbit by a 2 000-N gravitational force. Each time the satellite completes an orbit of circumference 80 000 km, the work done on it by gravity is: d. 0. (gravity is conservative, satellite returns to starting point) A golf ball hits a wall and bounces back at 3/4 the original speed. What part of the original kinetic energy of the ball did it lose in the collision? c. 7/16 (1² - (3/4)²) If during a given physical process the only force acting on an object is friction, which of the following must be assumed in regard to the object’s kinetic energy? d. cannot tell from the information given (as in second question above) A very light cart holding a 300-N box is moved at constant velocity across a 15-m level surface. What is the net work done on the box in this process? a. zero (no change in KE) A 7.00-kg bowling ball falls from a 2.00-m shelf. Just before hitting the floor, what will be its kinetic energy? (g = 9.80 m/s2 and assume air resistance is negligible) d. 137 J (mgh) As an object is lowered into a deep hole in the surface of the earth, which of the following must be assumed in regard to its potential energy? b. decrease When an object is dropped from a tower, what is the effect of the air resistance as it falls? d. None of the above choices are valid. The were: does positive work, increases the object’s kinetic energy, increases the object’s potential energy A 2.00-kg ball has zero kinetic and potential energy. Ernie drops the ball into a 10.0-m-deep well. Just before the ball hits the bottom, the sum of its kinetic and potential energy is: a. zero. (Energy conservation – assuming no air friction)A 2.00-kg ball has zero potential and kinetic energy. Maria drops the ball into a 10.0-m-deep well. After the ball comes to a stop in the mud, the sum of its potential and kinetic energy is: c. −196 J. (mgh; the only negative answer) Two blocks are released from the top of a building. One falls straight down while the other slides down a smooth ramp. If all friction is ignored, which one is moving faster when it reaches the bottom? c. They both will have the same speed. (Energy conservation) A Hooke’s law spring is mounted horizontally over a frictionless surface. The spring is then compressed a distance d and is used to launch a mass m along the frictionless surface. What compression of the spring would result in the mass attaining double the kinetic energy received in the above situation? a. 1.41 d (spring energy ~ compression²) I drop a 60-g golf ball from 2.0 m high. It rebounds to 1.5 m. How much energy is lost? a. 0.29 J (mg times difference in height) A force of 5.0 N is applied to a 20-kg mass on a horizontal frictionless surface. As the speed of the mass increases at a constant acceleration, the power delivered to it by the force: b. increases. (power = F v) A 100-W light bulb is left on for 10.0 hours. Over this period of time, how much energy was used by the bulb? c. 3 600 000 J (watts times time in seconds) A car wash nozzle directs a steady stream of water at 1.5 kg/s, with a speed of 30 m/s, against a car window. What force does the water exert on the glass? Assume the water does not splash back. b. 45 N (momentum transfer/time) A moderate force will break an egg. However, an egg dropped on the road usually breaks, while one dropped on the grass usually doesn’t break. This is because for the egg dropped on the grass: c. the time interval for stopping is greater. (so F = momentum transfer/time is less) A lump of clay is thrown at a wall. A rubber ball of identical mass is thrown with the same speed toward the same wall. Which statement is true? b. The ball experiences a greater change in momentum than the clay. (because its velocity changes from positive to negative)Object 1 has twice the mass of Object 2. Each of the objects has the same magnitude of momentum. Which of the following statements is true? c. One object has twice the kinetic energy of the other. (KE = p²/2m) A billiard ball is moving in the x-direction at 30.0 cm/s and strikes another billiard ball moving in the y-direction at 40.0 cm/s. As a result of the collision, the first ball moves at 50.0 cm/s, and the second ball stops. What is the change in kinetic energy of the system as a result of the collision? a. 0 (3² + 4² = 5²) During a snowball fight two balls with masses of 0.4 and 0.6 kg, respectively, are thrown in such a manner that they meet head-on and combine to form a single mass. The magnitude of initial velocity for each is 15 m/s. What is the speed of the 1.0-kg mass immediately after collision? b. 3 m/s (formula for inelastic collision) A billiard ball collides in an elastic head-on collision with a second identical ball. What is the kinetic energy of the system after the collision compared to that before collision? a. the same as (elastic means KE is conserved) In a two-body collision, if the kinetic energy of the system is conserved, then which of the following best describes the momentum after the collision? b. must also be conserved (momentum is ALWAYS conserved in a collision) Two objects, one less massive than the other, collide elastically and bounce back after the collision. If the two originally had velocities that were equal in size but opposite in direction, then which one will be moving faster after the collision? a. The less massive one. (has the greater speed) A 5-kg object is moving to the right at 4 m/s and collides with another object moving to the left at 5 m/s. The objects collide and stick together. After the collision, the combined object: d. has less kinetic energy than the system had before the collision (stick together inelastic energy loss independent of the numbers) Starting from rest, a wheel undergoes constant angular acceleration for a period of time T. At which of the following times does the average angular acceleration equal the instantaneous angular acceleration? d. all of the above (If quantity is constant, average always equals that constant value) Consider a point on a bicycle
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