2The unit for work is Joules The unit for work is Joules. What is an equivalent unit for work using meters, kilograms, and seconds?kg m/s2kg m2/skg m2/s2kg2m/s2c) kg m2/s2
3If someone pushes a stationary brick wall ten times harder than they did yesterday, what happens to the work done? (Increase, Decrease or Stay the same.)Stay the same
4A 4. 0 kg mass is moving with a speed 2. 0 m/s. A 1 A 4.0 kg mass is moving with a speed 2.0 m/s. A 1.0 kg mass is moving with speed 4.0 m/s. Both objects encounter the same constant braking force and are brought to rest. How do their stopping distances compare?They are the same.ΔKE = W ΔKE = W½ 4(2)2 = Fd ½ 1(4)2 = Fd8/F = d /F = d
5An object hits a wall and bounces back with half its original speed An object hits a wall and bounces back with half its original speed. What is the ratio of the final kinetic energy to the initial kinetic energy?1/4
6At what rate is a 60 kg boy using energy when he runs up a flight of stairs 10 m high in 8 seconds?
7A 10 kg mass is moving with a speed of 4. 0 m/s A 10 kg mass is moving with a speed of 4.0 m/s. How much work is required to stop the mass?80 J W = ΔKE = ½ mv2 = ½ (10)(42)
8You slam on the brakes of your car and skid a certain distance You slam on the brakes of your car and skid a certain distance. If you had been traveling twice as fast, what distance would the car have skidded under the same conditions?Four times farther.
9An object that has kinetic energy must have: (mark all that apply) MomentumAccelerationA force applied to itPotential Energya) Momentum
10a) KE increases and PE decreases An acorn falls from a tree. Compare its kinetic energy to its potential energy.KE increases and PE decreasesKE decreases and PE decreasesKE increases and PE increasesKE decreases and PE increasesa) KE increases and PE decreases
11Car J moves twice as fast as car K and has half the mass of car K Car J moves twice as fast as car K and has half the mass of car K. What is the ratio of car J’s kinetic energy to car K’s kinetic energy?2 to 1
12They rise to the same height. A lightweight object and a very heavy object are sliding with equal speeds along a level frictionless surface. They both slide up the same frictionless hill. Which rises to a greater height?They rise to the same height.
13A 1. 0 kg ball falls to the floor. When it is 0 A 1.0 kg ball falls to the floor. When it is 0.70 m above the floor, its potential energy exactly equals its kinetic energy. How fast is it moving?3.7 m/s
14A ball falls from the top of a building, through the air (air friction is present) to the ground below. How does the KE just before striking the ground compare to the PE at the top of the building?PEmax > KEmax
15How many joules of energy are used by a 1. 0 hp motor that runs for 1 How many joules of energy are used by a 1.0 hp motor that runs for 1.0 hr? (1 hp = 746 W)2,685,600 J
16If a skater’s speed increases so he has twice the momentum, then his kinetic energy increases by what factor?Four
17Consider molecules of hydrogen gas and molecules of heavier oxygen gas that have the same kinetic energy. Which molecules have a greater speed?hydrogen gas