Negative work can be done
a. by friction on the tires while a car is accelerating without skidding.
b. by a spring at the bottom of an elevator shaft when it stops a falling elevator.
c. by a hand catching a ball.
d. by all of the above.
e. only by (b) and (c) above.
e
You might also like to view...
Air at 20°C flows at 1 m/s between two parallel flat plates spaced 5 cm apart. Estimate the distance from the entrance to the point at which the hydrodynamic boundary layers meet.
GIVEN
Air flows between two parallel flat plates
Air speed (U?) = 1 m/s
Distance between the plates (D) = 5 cm = 0.05 m
Air temperature = 20°C
FIND
The distance from the entrance (X1) where the boundary layers meet
ASSUMPTIONS
Steady state
Laminar flow
SKETCH
Some of Jupiter's smaller outer moons have retrograde orbits, indicating capture occurred
Indicate whether the statement is true or false
Minimal orbit speed about Earth is about 8 km/s. Minimal orbital speed for a satellite about Jupiter would be
A) less than 8 km/s. B) greater than 8 km/s. C) about 8 km/s.
As an object moves from point A to point B only two forces act on it: one force is nonconservative and does ?30 J of work, the other force is conservative and does +50 J of work. Between A and B,
a. the kinetic energy of object increases, mechanical energy decreases. b. the kinetic energy of object decreases, mechanical energy decreases. c. the kinetic energy of object decreases, mechanical energy increases. d. the kinetic energy of object increases, mechanical energy increases. e. None of the above.