wrench thrown downward from 128' at 32'/sec; height given by

[leahacarson]

I am so lost! I don't know how to put this in the right type of equation or how to solve it. Could someone please help me get started?

92.Throwing a wrench. An angry construction worker throws his wrench downward from a height of 128 feet with an initial velocity of 32 feet per second. The height of the wrench above the ground after t seconds is given by S(t)=-16^2-32t+128.

1.What is the height of the wrench after 1 second? I think the answer is 48 feet but my instructor told me I was wrong

2.How long does it take for the wrench to reach the ground?
I think it would take about 2 seconds....

 

[Deleted member 4993]

Re: Word Problem Help Please

I am so lost! I don't know how to put this in the right type of equation or how to solve it. Could someone please help me get started?

92.Throwing a wrench. An angry construction worker throws his wrench downward from a height of 128 feet with an initial velocity of 32 feet per second. The height of the wrench above the ground after t seconds is given by S(t)=-16^2-32t+128.


1.What is the height of the wrench after 1 second? I think the answer is 48 feet but my instructor told me I was wrong

How did you get "48" - please show work.
2.How long does it take for the wrench to reach the ground?
I think it would take about 2 seconds....

How did you get "2" - please show work.

 

[chivox]

Height of a wrench from an angry construction worker

I am so lost! I don't know how to put this in the right type of equation or how to solve it. Could someone please help me get started?

92.Throwing a wrench. An angry construction worker throws his wrench downward from a height of 128 feet with an initial velocity of 32 feet per second. The height of the wrench above the ground after t seconds is given by S(t)=-16^2-32t+128.


1.What is the height of the wrench after 1 second? I think the answer is 48 feet but my instructor told me I was wrong


2.How long does it take for the wrench to reach the ground?
I think it would take about 2 seconds....

First thing to do online here is make sure you typed the formula correctly. I think we're missing a "t" or parentheses somewhere. Please double-check the formula, and use extra parentheses if required to tell us what is raised to the second power. Is it supposed to be t^2 or 16^2 in the first term?

For part 1, take a step back and look at the problem. If the wrench starts out at 32 ft/sec, accelerates at 32 ft/sec^2, both in the negative direction of course, its velocity after one second is 64 ft/sec, and during that first second, it accelerated from 32 to 64 ft/sec at a uniform rate. The average velocity, therefore, is 48 ft/sec, meaning the wrench traveled 48 ft in that first second, down from its original position. I think all you're missing is a subtraction from the original height. Do you see what I mean? You actually have to figure in the 128 ft as the original height. Try to show your work and where the 48 came from, and then the reason why that's the wrong answer should be obvious to you.

Try to show your work for the second part as well. Don't just guess. You've got a formula, so it's time to use that formula. What do you have to solve for. When it says "the wrench to reach the ground" what does that mean in terms of what you have to set your equation equal to?

 

[Denis]

Re: Word Problem Help Please

...or buy a wrench and start throwing it :wink: