Physics Work and Energy Quiz 6C Energy Conservation

A heavy dart and a light dart are launched vertically by identical ideal springs. Both springs were initially compressed by the same amount. There is no significant air resistance. Which of the following statements about these darts are correct? (There could be more than one correct choice.)

*a. The darts both have the same kinetic energy just as they move free of the spring.* *b. The lighter dart leaves the spring moving faster than the heavy dart.* c. The heavy dart had more initial elastic potential energy than the light dart. d. Both darts move free of the spring with the same speed. *e. Both darts had the same initial elastic potential energy.*

Which of the following is a true statement about the conservation of energy?

*a. Total energy is always conserved.* b. Mechanical energy is always conserved. c. Potential energy is always conserved. d. Kinetic energy is always conserved.

A 3.00 kg toy falls from a height of 1.00 m. The kinetic energy of the toy be just before the toy hits the ground is ___ J. (Assume no air resistance.)

29.4

When you drop a pebble from height H, it reaches the ground with kinetic energy K if there is no air resistance. From what height should you drop it so it will reach the ground with twice as much kinetic energy?

a. 4H b. square root of 2 H *c. 2H* d. 16H e. 8H

A girl throws a stone from a bridge. Consider the following ways she might throw the stone. The speed of the stone as it leaves her hand is the same in each case. Case A: Thrown straight up. Case B: Thrown straight down. Case C: Thrown out at an angle of 45° above horizontal. Case D: Thrown straight out horizontally. In which case will the speed of the stone be greatest when it hits the water below if there is no significant air resistance?

a. Case C b. Case D c. Case A d. Case B *e. The speed will be the same in all cases.*

Swimmers at a water park have a choice of two frictionless water slides, as shown in the figure. Although both slides drop over the same height h, slide 1 is straight while slide 2 is curved, dropping quickly at first and then leveling out. How does the speed v1 of a swimmer reaching the bottom of slide 1 compare with v2, the speed of a swimmer reaching the end of slide 2?

a. No simple relationship exists between v1 and v2. *b. v1 = v2* c. v1 < v2 d. The heavier swimmer will have a greater speed than the lighter swimmer, no matter which slide he uses. e. v1 > v2

The main difference between kinetic energy and potential energy is that

a. although both energies involve motion, only kinetic energy involves position. b. although both energies involve position, only potential energy involves motion. c. kinetic energy involves position, and potential energy involves motion. *d. kinetic energy involves motion, and potential energy involves position.*

Two objects, one of mass m and the other of mass 2m, are dropped from the top of a building. If there is no air resistance, when they hit the ground

a. both will have the same kinetic energy. b. the heavier one will have one-fourth the kinetic energy of the lighter one. *c. the heavier one will have twice the kinetic energy of the lighter one.* d. the heavier one will have four times the kinetic energy of the lighter one. e. the heavier one will have half the kinetic energy of the lighter one.

In the presence of frictional force,

a. nonmechanical energy is negligible and mechanical energy is conserved. b. nonmechanical energy is no longer negligible and mechanical energy is conserved. c. nonmechanical energy is negligible and mechanical energy is no longer conserved. *d. nonmechanical energy is no longer negligible and mechanical energy is no longer conserved.*