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UMD PHYS 121 - Practice Problems

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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? a. 40.0 J b. 126 J c. 251 J d. 0 The work done by static friction can be: a. positive. b. negative. c. zero. d. Any of the above. 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: a. 1.6 x 108 J. b. 1.6 x 1011 J. c. 6.4 x 1011 J. d. 0. 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? a. 1/4 b. 3/8 c. 7/16 d. 9/16 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? a. decreases b. increases c. remains constant d. cannot tell from the information given 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 b. 1/20 J c. 20 J d. 2 000 JA 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) a. 14.0 J b. 19.6 J c. 29.4 J d. 137 J 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? a. increase b. decrease c. remain constant d. cannot tell from the information given When an object is dropped from a tower, what is the effect of the air resistance as it falls? a. does positive work b. increases the object’s kinetic energy c. increases the object’s potential energy d. None of the above choices are valid. 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. b. 196 J. c. −196 J. d. 392 J. 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: a. zero. b. 196 J. c. −196 J. d. 392 J. 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? a. The block that went straight down. b. The block that went down the ramp. c. They both will have the same speed. d. Insufficient information to work the problem.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 b. 1.73 d c. 2.00 d d. 4.00 d 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 b. 0.50 J c. 0.88 J d. 1.0 J 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: a. remains the same. b. increases. c. decreases. d. doubles every 4.0 seconds. 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? a. 1 000 J b. 3 600 J c. 3 600 000 J d. 1.34 hp 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. a. 11 N b. 45 N c. 110 N d. 440 N 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: a. the change in momentum is greater. b. the change in momentum is less. c. the time interval for stopping is greater. d. the time interval for stopping 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? a. The clay experiences a greater change in momentum than the ball. b. The ball experiences a greater change in momentum than the clay. c. The clay and the ball experience the same change in momentum. d. It is not possible to know which object has the greater change in momentum. 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? a. Both objects can have the same kinetic energy. b. One object has 0.707 times the kinetic energy of the other. c. One object has twice the kinetic energy of the other. d. One object has 4 times the kinetic energy of the other. 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 b. some positive value c. some negative value d. No answer above is correct. 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? a. zero b. 3 m/s c. 6 m/s d. 9 m/s 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 b. one fourth c. twice d. four times 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? a. must be less b. must also be conserved c. may also be conservedd. is doubled in value Two objects, one less massive than the other, collide …


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UMD PHYS 121 - Practice Problems

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