Conservation of Energy AP Physics

Bowling Ball A is dropped from a point halfway up a cliff. A second identical bowling ball, B, is dropped simultaneously from the top of the cliff. Comparing the bowling balls at the instant they reach the ground, which of the following are correct? Neglect air resistance.

• Ball A has half the kinetic energy and takes half the time to hit the ground as Ball B.

• Ball A has half the kinetic energy and takes one-fourth the time to hit the ground as Ball B.

• Ball A has half the final velocity and takes half the time to hit the ground as Ball B.

• Ball A has one-fourth the final velocity and takes one-fourth the time to hit the ground as Ball B.

• None of these are correct.

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NGSS.HS-PS2-1

NGSS.HS-PS2-4

A system consists of two objects having masses m_l and m₂ (m_l < m₂). The objects are connected by a massless string, hung over a pulley as shown, and then released. When the object of mass m₂ has descended a distance h, the potential energy of the system has decreased by...

• (m₂ - m_l)gh

• m₂gh

• (m₁ + m₂)gh

• none of these

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NGSS.HS-PS2-1

NGSS.HS-PS3-1

A block on a horizontal frictionless plane is attached to a spring, as shown. The block oscillates along the x-axis with amplitude A. Which of the following statements about energy is correct?

• The kinetic energy of the block is at a minimum at x =0.

• The potential energy of the spring is at a minimum at x = A.

• The potential energy of the spring is at a minimum at x = 0.

• The kinetic energy of the block is at a maximum at x = A.

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NGSS.HS-PS3-2

Bob (80 kg) uses 180 N of force to get him up the slope. The vertical distance is 2 m and the diagonal is 10 m. Calculate the work he does.

• 1600 J

• 160 J

• 3600 J

• 1800 J

If the net work done on an object is negative, then the object’s kinetic energy...

• decreases

• remains the same

• increases

• is zero

Groot rescues Rocket from the bottom of a deep pit. Groot expends 1000 J of energy lifting Rocket who has a mass of 50 kg out of the pit. How deep is the pit?

• 0.5 m

• 2 m

• 4 m

• 10 m

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NGSS.HS-PS2-1

A 1-kg object is released from rest at the top of a rough-surfaced incline. The object slides without rotating to the bottom of the incline. The object’s kinetic energy at the bottom must be...

• equal to the block’s gravitational potential energy when it was released, because total mechanical energy must be conserved.

• equal to the block’s gravitational potential energy when it was released, because the gain in kinetic energy compensates for the mechanical energy lost to thermal energy on the rough incline.

• less than the block’s gravitational potential energy when it was released, because the gravitational potential energy was converted both to thermal energy and to kinetic energy.

• less than the block’s gravitational potential energy when it was released, because the work done by the friction force must be greater than the block’s gain in kinetic energy.

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NGSS.HS-PS3-4

A 10-kg wagon moves horizontally at an initial speed of 5 m/s. A 30-N force is applied to the wagon by pulling the rigid handle, which is angled 60° above the horizontal. The wagon continues to move horizontally for another 20 m. A negligible amount of work is converted into thermal energy. By how much has the wagon’s kinetic energy increased over the 20 m?

• 300 J

• 600 J

• 125 J

• 63 J

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NGSS.HS-PS2-1

NGSS.HS-PS3-1

The following graphs, all drawn to the same scale, represent the net force F as a function of displacement x for an object that moves along a straight line. Which graph represents the force that will cause the greatest change in the kinetic energy of the object from x = 0 to x = x₁?

• 
• 
• 
• 

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NGSS.HS-PS2-1

NGSS.HS-PS3-1

How are work and energy related?

• The work done by an external force acting on an object causes a change in the mechanical energy of the object.

• Work is the same thing as energy. They are equal.

• Energy is mgh, and work is mv²/2

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NGSS.HS-PS2-1