The object at rest has an initial velocity >0?

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SUMMARY

The discussion centers on a physics problem involving a grasshopper that jumps 1.00 m at a 45.0-degree angle with an initial speed of 3.13 m/s. The maximum height achieved by the grasshopper is 0.250 m. Participants clarify that the term "from rest" does not imply an initial velocity of zero at the moment of the jump, but rather indicates the grasshopper's state prior to the jump. The confusion arises from the phrasing of the problem, which could be improved for clarity.

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Homework Statement


A grasshoopper jumps 1.00 m from rest, with an initial velocity at a 45.0 degree angle with respect to the horizontal.
Find the initial speed of the grasshopper (answer is 3.13 m/s)
The maximum height reached (answer is .250m)


Homework Equations


acceleration in the x direction is considered constant, so you are using the basic kinematic equations, with a simplified equations for x vector components, e.g.
V0x=cos(0)

The Attempt at a Solution


The problem is that I can't figure out what they are asking. For example, up until now, in the class we have described an object at rest to have an initial velocity of zero. The question itself seems somewhat contradictory to me. What am I missing?
 
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Who said:
acceleration in the x direction is considered constant...

Velocity in x direction is considered constant. Velocity in y direction is changing due to gravity. You just need to find the components, and then, using basic kinematic equations, find maximum height, distance, initial velocity, time...

Take a look at http://www.ngsir.netfirms.com/englishhtm/ThrowABall.htm" .
 
Last edited by a moderator:
Who said:
The problem is that I can't figure out what they are asking. For example, up until now, in the class we have described an object at rest to have an initial velocity of zero. The question itself seems somewhat contradictory to me. What am I missing?
It's just an oddly phrased question. Despite the use of "from rest", they don't intend for the grasshopper to have an initial velocity of zero when he jumps. He was "at rest" sometime before he jumped. :wink:

A better phrasing would be something like: "A grasshopper jumps 1.00 m from its initial position, with an initial velocity at a 45.0 degree angle with respect to the horizontal."
 

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