I am having trouble with a relative velocity exercise. If any of you could bring some light on it i would be very happy.
The exercise as it is on the book:
The relative velocity of a butterfly and a bat with respect to the ground are 10 m/s and 20m/s, respectively. If the velocity of the bat relative to the butterfly is perpendicular to the velocity of the butterfly with respect to the ground, determine the angle which is formed between velocities with respect to the ground.
Asked
Active
Viewed 1,041 times
0
-
1Hi and welcome to the Physics SE! Please note that we don't answer homework or worked example type questions. Please see this Meta post on asking homework/exercise questions and this Meta post for "check my work" problems. You might want to consider posting on some other Physics website, such as the PhysicsForums. – stafusa Dec 08 '17 at 20:17
1 Answers
0
The wording of the question is very confusing. As with all problems which are difficult to imagine, start by drawing a suitable diagram. In this case, you need to draw the vector triangle.
If butterfly A and bat B have velocities $\vec{v_A}, \vec{v_B}$ then the velocity of B relative to A is $\vec{v_{BA}} = \vec{v_B} - \vec{v_A} = \vec{v_B} + (-\vec{v_A})$ . In other words, $\vec{v_{A}} + \vec{v_BA} = \vec{v_B}$.
The question is saying that the angle between $\vec{v_{BA}}$ and $\vec{v_A}$ is 90 degrees, and it is asking for the angle between $\vec{v_B}$ and $\vec{v_A}$. This is quite easy to work out because you have a right-angled triangle and you know the lengths of two sides.
sammy gerbil
- 27,277
-
okay, i wasn't sure how to represent the relative velocity vector with respect to the other velocities, but that got it clear. Thanks! – slothgena Dec 09 '17 at 23:50