5. If the speed of an object is halved, its kinetic energy will
(a) halve
(b) quarter
(c) quadruple
(d) increase 1.4 times
6. An apple fell out of a tree. On the descent, the apple lost 50 joules of potential energy and gained 40 joules of kinetic energy. Which of the following statements about the apple must be true?
(a) air resistance did affect the ball. The work against air resistance was 10 joules
(b) air resistance is negligible
(c) the total mechanical energy of the apple was always 90 joules
(d) the total mechanical energy of the ball decreased
7. A motorcyclist started at the top of a 30 meter high cliff with zero velocity. The mass of the motorcycle and the rider combined is 500 kilograms. If the motorcyclist zooms down the cliff, how much kinetic energy will the rider and cycle have at the bottom if 9000 joules of work was done against friction and the engine supplied 12,000 joules of work to the rider and cycle?
(a) 147 kilojoules
(b) 138 kilojoules
(c) 144 kilojoules
(d) 153 kilojoules
8. A 20-newton block is at rest at the bottom of a frictionless inclined plane. How much work must be done against gravity (potential energy gained) to move the block to the top of the incline?
(a) 40 joules
(b) 80 joules
(c) 100 joules
(d) 10 joules
9. A toy gun is loaded by pushing the toy dart (mass of m kilograms) into the gun and compressing the spring with a spring constant of k inside by a distance d. When the trigger is pulled, how fast will the dart leave the barrel of the gun?