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Math Help - Trig Help Word Problem

  1. #1
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    Trig Help Word Problem

    I just don't get these type of problems at all. Please help if at all possible the problem is as follows:

    An astronaut on the moon tosses a ball upwards; when will the ball initially be 35 feet above the lunar surface if the ball's height(feet) follows:
    -2.6t^2 + 32.1t + 5.5 and t is in seconds from release?
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  2. #2
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    Quote Originally Posted by tricey36 View Post
    I just don't get these type of problems at all. Please help if at all possible the problem is as follows:

    An astronaut on the moon tosses a ball upwards; when will the ball initially be 35 feet above the lunar surface if the ball's height(feet) follows:
    -2.6t^2 + 32.1t + 5.5 and t is in seconds from release?
    The height h(t)=-2.6t^2+32.1t+5.5

    Since we are given a height we set h(t)=35 to get

    35=-2.6t^2+32.1t+5.5 \iff 0=-2.6t^2+32.1t-29.5

    We can multiply the equation by 10 to eliminate the decimals

    0=-26t^2+321t-295 we can then factor this to get (you could also use the quadratic formula)

    -(t-1)(26t-295)=0 so t=1 or t=\frac{295}{26}\approx 11.3

    Good luck.
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  3. #3
    Rhymes with Orange Chris L T521's Avatar
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    Quote Originally Posted by tricey36 View Post
    I just don't get these type of problems at all. Please help if at all possible the problem is as follows:

    An astronaut on the moon tosses a ball upwards; when will the ball initially be 35 feet above the lunar surface if the ball's height(feet) follows:
    -2.6t^2 + 32.1t + 5.5 and t is in seconds from release?
    First, I don't see how we need trig here...

    All you need to do here is set 35=-2.6t^2+32.1t+5.5 and solve for t [this is a quadratic that can be easily solved using the quadratic equation].

    Note that you'll get two values both of which should be positive. The smaller value of t tells you the time it takes to initially reach the height of 35 feet (before reaching the maximum height). The second t value tells you when it reaches a height of 35 after it has reached its maximum height and starts to fall back to the surface.

    If you still have questions, feel free to ask.

    --Chris
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