Question

Two balls are dropped simultaneously from the same height. Ball A has three times the mass of Ball B. Assume air resistance is negligible.

1) Which combination of statements is most accurate? [Enter your answer as a string of the letter options you believe are correct. For instance, if you think options A, D, and E are correct, then enter "ADE". NOTE: There are only 5 tries for this problem.]

A) The KE of both balls is the same throughout the drop since they have the same acceleration.
B) The balls both have the same speed at each moment of the drop.
C) Doubling the height of the drop would double the final speed of either ball before impact.
D) Doubling the height of the drop would double the KE of each ball before impact.
E) None of the above

2) Which combination of statements is most accurate? [Enter your answer as a string of the letter options you believe are correct. For instance, if you think options A, D, and E are correct, then enter "ADE". NOTE: There are only 5 tries for this problem.]

A) Increasing the separation between two massive objects increases the GPE of the objects.
B) Steadily lowering a ball to the ground decreases GPE while increasing the ball's KE due to energy conservation.
C) Energy conservation means that if a system is isolated, its KE and GPE always transform into each other.
D) Momentum conservation and energy conservation are independent principles of physics.
E) None of the above

Answer 1

1) The speed of both balls is same at any instant since they both experience same acceleration. But KE is different as they have different masses. Final speed is v = sqrt(2gh). So doubling the height doesn't double the speed.

KE = mgh where m =mass of exch object. So doubling the height doubles the KE.

So, correct sequence is BD

2) A is correct. If the ball is being lowered steadily then, it's speed is constant, so KE is constant. So B is wrong.

For an isolated system, mechanical energy = KE+PE remains constant and KE and PE always transform into one another to make the mechanical energy constant. So C is correct.

Energy conservation doesn't necessarily mean conservation of momentum. So, they are independent.

So correct answer is ACD

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