Kinematics rope question

In summary, the problem involves finding the initial height above the water of a girl who swings on a rope, given her initial velocity and angle at release and the time she is in flight. The correct method is to use the equation H= -g/2 t2+ v0 sin(theta) t+ y0 and solve for y0 by plugging in the given information and setting H to 0.
  • #1
Mesmer17
5
0
Q)On a hot summer day a young girl swings on a rope above the local swimming hole (Figure 4-20). When she let's go of the rope her initial velocity is 2.05 m/s at an angle of 35.0° above the horizontal. If she is in flight for 1.60 s, how high above the water was she when she let go of the rope?

TO GET THE ANSWER.. first I found Vo by using 2.05(sin35) which is 1.17.. then I got the Vy by using -G(t) which is -9.80(1.60) which I got 15.68 for.. using these values I plugged them into the equation: H=Vy^2-Voy^2/2Ay and I got 12.5 for an answer that is wrong.. can anyone tell me where I went wrong? THANKS
 
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  • #2
Kinematics

Use the equation Vy= Voy + at to find Vy. You only multiplied a by t, so your Vy term was incorrect. Good luck
 
  • #3
Since you are told that "she is in flight for 1.60 s", don't you think it would be a good idea to use that information?

The simplest way to do this problem is to note that the height at time t is H= -g/2 t2+ v0 sin(theta) t+ y0 where H is the height above the water and y0 is the initial height above the water (which is what you are asked for).

When she hits the water, H= 0 so plug in the information you are given and solve -g/2 t2+ vo sin(theta)+ y0= 0 for y0.
 

1. What is kinematics in relation to rope?

Kinematics is the branch of physics that studies the motion of objects without considering the forces that cause the motion. In the case of rope, kinematics deals with the description of its movement and position over time without taking into account the tension or weight of the rope.

2. How do you calculate the speed of a rope?

The speed of a rope can be calculated by dividing the length of the rope by the time it takes for the rope to travel that distance. This calculation assumes that the rope is moving at a constant speed.

3. Can the shape of a rope affect its kinematics?

Yes, the shape of a rope can affect its kinematics. When a rope is bent or curved, its movement and position can be altered. This is because the rope is no longer moving in a straight line, which can change its speed and direction.

4. How does the tension of a rope impact its kinematics?

The tension of a rope can greatly impact its kinematics. The tension in a rope is caused by forces acting on the rope, such as weight or pulling forces. This tension can change the speed and direction of the rope's movement, making it an important factor to consider in kinematics.

5. Can kinematics equations be used to predict the movement of a rope?

Yes, kinematics equations can be used to predict the movement of a rope. These equations describe the relationship between an object's position, velocity, and acceleration over time, which can be applied to the movement of a rope. However, it is important to note that these equations may not be accurate if there are external forces acting on the rope, such as wind or friction.

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