Solving Constant Acceleration with Initial Speed & Time: Find Distance & Time

[jazzguitarist]

Homework Statement

A body has a constant acceleration of +5 ft/s^2, an initial speed of -10 ft/s, and a time travel of 4 seconds.
A)Find the total distance covered
B)Find the time at which the body has an instantaneous speed of zero

Homework Equations

speed=distance/time
distance=speed/time
v=v(initial) + at
v^2 - v(initial)^2 / 2a

The Attempt at a Solution

A) I tried using the formula to solve for delta x
(After getting v=10)
100 - (-100) \2a =200/10 = 20ft (would this be the total distance, assuming x(initial) is at zero?)

B) I have no idea if this is the right way, but this was my attempt.
0=-10 + (5)(4)
0= -10 + 20
10=20
20/10 = 2 seconds?

Any help would be greatly appreciated, I am new to physics and I feel at a loss setting up some of the problems.
Thank you.

 

[ehild]

The Attempt at a Solution

A) I tried using the formula to solve for delta x
(After getting v=10)
100 - (-100) \2a =200/10 = 20ft (would this be the total distance, assuming x(initial) is at zero?)

Δx=(v^2-v^2_(initial))/(2a)
V_initial is negative, but its square is positive. (-10)^2=100.

B) I have no idea if this is the right way, but this was my attempt.
0=-10 + (5)(4)
0= -10 + 20
10=20
20/10 = 2 seconds?

The time is asked so it is not 4 s. Your equation is 0=-10+5 t. Solve for t.

ehild