# Can someone check my answers on these kinematics questions?

dnt
I think I am doing them right but they don't match the answers that were supplied to me - i think the

1. A bike accelerates uniformly from rest to a speed of 7.10 m/s over a distance of 35.4 m.

Determine the acceleration of the bike.

my answer: I used the formula v^2 = vo^2 + 2ad and got a = .712 m/s^2

2. A car traveling at 22.4 m/s skids to a stop in 2.55 s. Determine the skidding distance of the

car (assume uniform acceleration).

my answer: I solved for acceleration first (-8.78 m/s^2) then used d=Vot + 1/2(a)t^2 to get

d = 28.57 m.

3. A bullet is moving at a speed of 367 m/s when it embeds into a lump of moist clay. The bullet

penetrates for a distance of 0.0621 m. Determine the deceleration of the bullet when moving into

the clay.

my answer: I used the formula v^2 = vo^2 + 2ad and got a = -1.08 x 10^6 m/s. (my issue

here is that the answer should be negative, not positive. right?)

4. A dragster accelerates to a speed of 112 m/s over a distance of 398 m. Determine the

acceleration of the dragster.

my answer: Once again I used the formula v^2 = vo^2 + 2ad (with Vo = 0; at least I assume

that is true) and got a = 15.76 m/s^2.

I think my equations and answers are right but if not, can someone help me out and correct me where I have made mistakes.
Thanks.

Atomos
The reasoning to all of your answers makes sense, I did not check the actuak numeric values to the answers though.

dnt
can someone else check the answers to make sure they are correct? thanks.

Homework Helper
#1, you got it right.
#2, wrong a little bit, it's exactly : d = 28.56 m (not d = 28.57 m). But 0.01 m would be negligible.
#3 is correct exept that it should be a = -1.08 x 106 m/s2, (not -1.08 x 106 m/s) :).
#4 is also correct.
Viet Dao,

dnt
thanks viet.