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Question 9 of 36

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SAT Subject Test

Each option presents a graph. The horizontal axis is labeled t and the vertical axis is labeled v. The origin is labeled O.  The plot is a straight line starting at the origin and extending diagonally upward to the right.

A block is pulled along a horizontal surface with a constant horizontal force of magnitude F. The surface exerts a frictional force of constant magnitude f on the block. The graph of speed v as a function of time t for the block is shown above.

If, instead, the block slides without friction but is pulled with the same horizontal force of magnitude F, which of the following would be a possible new graph of speed v as a function of time t? (The dashed line represents the old graph.)

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The plot shows two straight lines, a solid line and a dashed line, both starting at the origin and extending diagonally upward to the right. The solid line has a steeper slope than the dashed line.

Correct Answer: 
Yes

The plot shows two straight lines, a solid line and a dashed line, both starting at the origin and extending diagonally upward to the right. The dashed line has a steeper slope than the solid line.

Correct Answer: 
No

A graph shows a straight dashed line starting at the origin and extending diagonally upward to the right. A concave down curve starts at the origin and extends up and to the right, at first with a steeper slope than the dashed line, and then curving back down to meet the end of the dashed line.

Correct Answer: 
No

A graph shows a straight dashed line starting at the origin and extending diagonally upward to the right. A concave up curve starts at the origin and extends up and to the right, at first with a smaller slope than the dashed line and then curving back up to meet the end of the dashed line.

Correct Answer: 
No

The plot shows a straight dashed line starting at the origin and extending diagonally upward to the right. A straight solid line is shown parallel to the dotted line, starting at a point slightly below halfway up the vertical axis.

Correct Answer: 
No

The correct answer is (A). Without friction, there is still a constant force on the block. This means a constant acceleration, so the speed curve will still be a straight line. Removing friction will not cause the block to be in motion before it is pulled, so the initial speed remains zero. Finally, since friction would act against the pulling force, the net force on the block is greater without friction, so the acceleration and thus the slope of the speed graph would be greater

Question Difficulty: 
easy