Unit: Motion in a Plane
Year: 1997 Question#: 61
Question: A baseball player throws a baseball at a speed of 40meters per second at an angle of 30 to the ground. The horizontal component of the baseball's velocity is approximately:
(1 ) 15m/s
(2 ) 20m/s
(3 ) 30m/s
(4 ) 35m/s
What is this question really asking?
Explanation by: Julie D.
[ Return to question menu ]
Answer 1
15m/s
INCORRECT
return to top
Answer 2
20m/s
INCORRECT
You may have calculated this using the sine of the angle instead of the cosine of the angle.
return to top
Answer 3
30m/s
INCORRECT
return to top
Answer 4
35m/s
CORRECT
The horizontal component of the velocity is the cosine of 30 degrees multiplied by 40m/s. The cosine of 30 degrees is the 0.8660 (check this on your Regents Reference Tables or on your calculator). To get the speed, multiply by 40m/s. This equals 34.64, which is approximately 35m/s.
return to top
What's this question really asking?
The question deals with resolving vectors into components. To resolve a vector into components, use trigonometry. The sine of the angle is the opposite divided by the hypotenuse, and the cosine of the angle is the adjacent divided by the hypotenuse. To find the length of a side set the sine or cosine equal to the corresponding ratio.
Ex. cos30=x/40 For vector components, this means that the
40cos30=x horizontal component is the hypotenuse length
34.64=x times the cosine of the angle (rcosq) and the vertical component is rsinq.
return to top
