1 ) Can work be done on a system if there is no motion? ( Yes, if an outside force is provided. Yes, since motion is only relative. ( ) No, since a system which is not moving has no energy ( ) No, because of the way work is defined. 2) If you walk 5 m horizontally forward at a constant velocity carrying a 10 N object, the amount of work done by the force holding up the object is ( ) > 50 J ( ) = 50 J ( ) < 50 J but more than OJ ( 0J 3) If the network done on an object is positive, then the object's kinetic energy () decreases ( ) remains the same() increases () is zero 4) An object hits a wall and bounces back with half of its original speed. What is the ration of the final kinetic energy to the initial kinetic energy? ( ) ( ) ( ) ( ) 4 5) Is it possible for a system to have negative potential energy? ( ) Yes, as long as the total energy is positive () Yes, since the choice of the zero of potential energy is arbitrary ( No, because the kinetic energy of a system must equal its potential energy ( No, because this would have no physical meaning. 6) A 0.2 kg mass attached to the end of a spring causes it to stretch 5 cm. If another 0.2 kg mass is added to the spring, the potential energy of the spring will be ( ) the same ( ) twice as much() 3 times as much () 4 times as much 7) You lift a 10 N book up in the air a distance of 1 m, at a constant velocity of 0.5 m/s. What is the work done by the weight of the book? ( ) +10 J ()-10 J ( ) +5J ()-5J 8) John pulls Jane in a sled on an icy surface (assume no friction), with a force of 60 N at an angle of 37° upward from the horizontal. If he pulls her a distance of 12 m, what is the work done by John? ( ) 185 J ( ) 433 J ( 575 J ( ) 720 J 9) When a car is braked to a stop, its kinetic energy is transformed to ( ) stopping energy ( ) potential energy ( ) energy of motion ( ) energy of rest () heat 10) Which has the greater kinetic energy, a car traveling at 30 km/h of a car of half the mass traveling at 60 km/h? ( the 30 km/h car ( the 60 km/h car ( both have the same kinetic energy 11) Which requires the most amount of work on the brakes of a car? () slowing down from 100 km/h to 70 km/h () slowing down from 70 km/h to a stop( both are the same 12) A horizontal force of 200 N is applied to move a 55 kg cart, initially at rest, across a 10 m level surface. What is the final speed of the cart? ( ) 73 m/s ( ) 36 m/s ( ) 8.5 m/s ( ) 6 m/s 13) A 400 N box is pushed up an inclined plane. The plane is 4 m long and rises 2 m. If the plane is frictionless, how much work was done by the push? ( ) 1600 J ( ) 800 J () 400 J ( ) 100 J
1) No, because of the way work is defined.
Work done = Force*displacement
If there is no motion means displacement is zero. So, there is
no work done.
2) 0 J
No work is done because the force you are exerting is not in the
same direction in which you are travelling.
If the net work done on an object is positive, then object’s
kinetic energy is increases because work done is defined as a
change in Kinetic energy.
We know that, KE = (1/2)mv^2
Initial kinetic energy, KEi = (1/2)mv^2
Now the speed is halved = v/2
Final Kinetic energy, KEf = (1/2)m*(v/2)^2
KEf/KEi = (1/2)m(v/2)^2 / (1/2)mv^2
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