# Motion with constant accln help.

• misogynisticfeminist
In summary, the conversation is about finding the time interval between when a missile is first level with the top of a tower and when it is again level with the tower. The initial velocity of the missile is 84m/s and the tower is 70m high. The individual is trying to solve the problem using a quadratic equation but realizes they misread the problem and the correct solution is to subtract the two answers.
misogynisticfeminist
This question is the first to pop out in the problems I'm supposed to do and I already have problems with it, so there must be a small little detail which i missed.

A missle is fired vertically upward with an initial velocity of 84m/s from a pt. level with a foot of a tower 70m high. Show that the time from when the missle is first level with the top of the tower until it is again level with the tower a 2nd time to be 15.4 seconds.

What i did was use $$s=ut-\frac{1}{2} gt^2$$ substituting, i get,

$$70=84t-1/2 gt^2$$

(are my signs correct)?

$$t= 0.87837 , t= 16.25286236$$

the 2nd answer is greater than the given answer of 15.4 seconds. and the first is way too small. I got a feeling i set up the equation wrong. Can anyone help?

thanks.

No, you read the problem wrong!

The problem does not ask for the time when the rocket is 70 feet high. It asks for the time interval BETWEEN the two times! Subtract!

OH ! i gettit, so i just take away the 2 answers i got. Thanks a lot !

## What is motion with constant acceleration?

Motion with constant acceleration is a type of motion where an object's velocity changes at a constant rate. This means that the object's speed increases or decreases by the same amount in each unit of time.

## What is the difference between acceleration and constant acceleration?

Acceleration is the rate at which an object's velocity changes. Constant acceleration is a specific type of acceleration where the rate of change in velocity remains the same over time. In other words, the object's acceleration does not fluctuate.

## How is constant acceleration calculated?

Constant acceleration is calculated using the equation a = (vf - vi) / t, where a is acceleration, vf is final velocity, vi is initial velocity, and t is time. This equation can be used to find any of the three variables as long as the other two are known.

## What are some examples of motion with constant acceleration?

Some examples of motion with constant acceleration include a car driving at a constant speed, a ball rolling down a hill, and a rocket launching into space. In all of these cases, the object's velocity is changing at a constant rate.

## What are the units of constant acceleration?

The units of constant acceleration are typically meters per second squared (m/s^2) in the metric system. In the imperial system, it can be expressed as feet per second squared (ft/s^2). These units represent the change in velocity over time.

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