# Kinematics in one dimension

1. Jun 14, 2007

1. The problem statement, all variables and given/known data

A football player, starting from rest at the line of scrimmage, accelerates along a straight line for a time of 3 seconds. Then during a negligible amount of time, he changes the magnitude of his acceleration to a value of 1.1 m/secondssquared. With this acceleration, he continues in the same direction for another 2 seconds until he reaches a speed of 6.4 m/sec. What's the value of his acceleration (assumed to be constant) during the initial 3 sec period?

2. Relevant equations

kinematics

3. The attempt at a solution

I tried drawing a graph but to no avail. How would I do it with just equations?

2. Jun 14, 2007

### Dick

You'll have to pick out an equation to use first. As you are given times, velocities and accelerations - something relating the three of those could be handy. Can you find one?

3. Jun 14, 2007

v=vinital+at
but i dont understand what 1.1 m/s sqrd is for....is that the acceleration during the 3sec-5sec time period? i dont know what to plug in

4. Jun 14, 2007

### Dick

Good equation choice and yes, that's what the 1.1m/sec^2 is. So first concentrate on the 3-5 sec period. You know the final velocity (at 5 sec) and you know the acceleration. Can you determine the velocity at 3 sec? BTW write the equation as v=vinitial+a*(t-tinitial) where tinitial is 3 sec for this time period.

Last edited: Jun 14, 2007
5. Jun 14, 2007

Ok, so I got that stuff plugged in but the acceleration isn't there...what would that be?

6. Jun 14, 2007

Ohhh ok, so 1.1 is the magnitude of the acceleration so that means it IS the acceleration from 3-5 seconds right?

7. Jun 14, 2007

### Dick

Right. You may find it easier to work with your equation in the form (change of v)=a*(change of t).

8. Jun 15, 2007

Ok, so i got 1.4 m/s^2 but i dont know if that's the right answer? can anyone do it and see what they get/help me? =)

9. Jun 15, 2007

### Dick

Yes, that's right.

10. Jun 15, 2007