โฑ๏ธ **2 min read**

#projectilemotion

#velocity

#acceleration

#gravity

#work

table of contents

written by

kanya shah

published on april 21, 2020

Last updated on June 11, 2020

1) A ball rolls off the edge of the table. The horizontal component of the ballโs velocity remains constant during its entire trajectory because

A: the ball is not acted upon by a force in the horizontal direction. B: the net force acting on the ball is zero.

C: the ball is not acted upon by any force.ย

D: the ball is not acted upon by any force in the vertical direction.ย

E: None of the other choices are correct.

**Answer:** The answer is A because thereโs no acceleration in the x direction when we deal with projectile motion. If the acceleration equals zero, then F = m*a has to be zero for the x direction.

2)

Image courtesy of AP Physics Walker Textbook.

The scale at the left is attached to the ceiling and a mass of 1.00 kg hangs from it. It reads 9.81 N. The identical scale at the right is connected by perfect springs passing over perfect pulleys to two 1.00 kg masses hanging vertically at the end of the strings. The scale at the right reads

A: exactly 19.62 N B: more than 19.62 N

C: more than 9.81 N

D: less than 9.81 N but quite twice as much

E: exactly 9.81 N

**Answer:** The answer is E because the scale at the left has gravity acting on the mass and the scale on the right also has gravity acting on the mass from the perfect pulley system. Since the scales and each side of the pulley are identical, it makes sense for both masses to have the same weight of 9.81 N.

3) A force produces power P by doing work W in a time T. What power will be produced by a force that does six times as much work in half as much time?

A: 12P B: 6P

C: 1/12 P

D: 3/8 P

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E: 1P

**Answer:** The answer is A, 12P because you need to rearrange the power formula.

Approach these problems with the concepts in mind and consider whether the answer is plausible or just a ridiculous option meant to distract you. Once you narrow it down to the last two choices, go back to the problem and reread whatโs being asked. Sometimes you can make a guess based on the context if you havenโt gotten the answer. If you donโt know how to solve the problem, you should guess using any clues from the units and questions to figure the answer out.

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