SMDEP Physics Conservation of Energy, Power

Friday’s Mechanics Quiz No calculators needed/allowed Don’t memorize formulas –Any formulas needed will be provided Mostly qualitative, conceptual questions Length: About 30 minutes Material: Kinematics, Mechanics, Energy –Circular motion, friction, springs –NOT: vectors, dot products, momentum No clickers needed Grades not instant Also: Midcourse evaluations –What would you change about the course?

Ch 8, #13: initial speed m/s m/s m/s m/s 5.Other 6.Didn’t finish

Ch 8, #29: final speed m/s m/s m/s m/s 5.Other 6.Didn’t finish

Ch 8, #59: power in hp hp hp hp hp 5.Other 6.Didn’t finish

Can potential energy be negative? 1.Yes 2.No

Can kinetic energy be negative? 1.Yes 2.No

Can total energy be negative? 1.Yes 2.No

A 1 kg mass and a 2 kg mass are tossed straight up into the air at the same time. The initial kinetic energies of the two masses are the same. Neglect air resistance. Which statement must be true? 1.The two masses reach the same maximum height. 2.The two masses must stay in the air the same amount of time. 3.The potential energies of the two masses are the same when they are at their maximum heights. 4.Two of the above 5.None of the above

Consider two blocks stacked on a table. Someone pulls the bottom block to the right with a rope in such a way that both blocks accelerate to the right but no slipping occurs at the interface between the blocks. Friction at the interface between the two blocks does: 0 of Positive work on the top block 2.Negative work on the top block 3.No work on the top block

A toy car is released at the top of a ramp. It rolls down the ramp converting potential energy into kinetic energy. It then rolls up an identical ramp converting kinetic energy into potential energy. In the real world, this back and forth motion does not continue forever, and eventually the car settles at the bottom of the ramp. This is because: 0 of Friction energy is not exactly conserved 2.Friction causes heat, which is not converted back to either kinetic or potential energy 3.If you wait long enough, energy is destroyed by the environment

A block initially at rest is allowed to slide down a frictionless ramp and attains a speed v at the bottom. To achieve a speed 2v at the bottom, how many times as high must a new ramp be? Same height 2.Twice as high 3.Four times as high 4.Half as high 5.One-fourth as high 6.Same height but twice as long 7.Same height but 4 times as long

Two marbles, one twice as heavy as the other, are dropped to the ground from the roof of a building. Just before hitting the ground, the heavier marble has: 0 of The same kinetic energy as the lighter one 2.Twice the kinetic energy of the lighter one 3.Half the kinetic energy of the other one 4.Four times the kinetic energy of the other one 5.Impossible to determine

Compared to the change in energy required to accelerate a car from rest to 10 miles per hour, the change in energy required to accelerate the car from 10 miles per hour to 20 miles per hour is: 1.The same 2.Twice as much 3.Three times as much 4.Four times as much 5.Need more information 0 of 5 :10