Energy Conservation in Physics

A bead is moving with a speed of 20 m/s at position A on the track shown in the figure. This track is friction-free, and there is no appreciable air resistance. What is the speed of the bead at point C?

• 0 m/s
• 34 m/s
• 69 m/s
• 20 m/s

Tags

NGSS.HS-PS3-1

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?

• v1 > v2
• v1 < v2
• v1 = v2
• The heavier swimmer will reach the bottom with more speed

A 60-kg skier pushes off the top of a frictionless hill with an initial speed of 4.0 m/s.  How fast will she be moving after dropping 10 m in elevation? Air resistance is negligible.

• 0.20 km/s
• 15 m/s
• 10 m/s
• 0.15 km/s

Tags

NGSS.HS-PS3-1

A heavy sled and a light sled, both moving horizontally with the same kinetic energy, suddenly slide onto a rough patch of snow and eventually come to a stop. The coefficient of kinetic friction between the sleds and the rough snow is the same for both of them. Which of the following statements about these sleds are correct? 

• The light sled will slide farther on the rough snow than the heavy sled.
• The heavy sled will slide farther on the rough snow than the light sled.
• Both sleds will slide the same distance on the rough snow before stopping.
• All the statements are correct

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NGSS.HS-PS2-1

A person stands on the edge of a cliff. She throws three identical rocks with the same speed. Rock X is thrown vertically upward, rock Y is thrown horizontally, and rock Z is thrown vertically downward. If the ground at the base of the cliff is level, which rock hits the ground with the greatest speed if there is no air resistance?

• Rock X
• Rock Y
• Rock Z
• They all hit the ground with the same speed.

Tags

NGSS.HS-PS2-1

NGSS.HS-PS2-4

A heavy frog and a light frog jump straight up into the air. They push off in such away that they both have the same kinetic energy just as they leave the ground. Air resistance is negligible. Which of the following statements about these frogs are correct?

• Just as they leave the ground, the heavier frog is moving faster than the lighter frog.
• Just as they leave the ground, the lighter frog is moving faster than the heavier frog.
• They both leave the ground with the same speed.
• The lighter frog goes higher than the heavier frog.

Tags

NGSS.HS-PS2-1

A prankster drops a water balloon from the top of a building. If the balloon is traveling at 29.1 m/s when it strikes a window ledge that is 1.5 m above the ground, how tall is the building? Neglect air resistance.

• 45 m
• 43 m
• 46 m
• 47 m

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NGSS.HS-PS2-4

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

• H
• 2H
• 4H
• 8H

Tags

NGSS.HS-PS2-4

A toy rocket that weighs 10 N blasts straight up from ground level with an initial kinetic energy of 40 J.  At the exact top of its trajectory, its total mechanical energy is 140 J.  To what vertical height above the ground does it rise, assuming no air resistance?

• 1.0 m
• 10 m
• 14 m
• 24 m

Tags

NGSS.HS-PS3-1

A certain car traveling at 34.0 mph skids to a stop in 29 meters from the point where the brakes were applied. In approximately what distance would the car have stopped had it been going 105.4 mph?

• 279 m
• 158 m
• 90 m
• 51 m

Tags

NGSS.HS-PS2-1