help The driver of a car slams on the brakes when he sees a tree blocking the ro

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The driver of a car slams on the brakes when he sees a tree blocking the road. The car slows uniformly with acceleration of -5.70 m/s2 for 4.30 s, making straight skid marks 60.1 m long, all the way to the tree. With what speed does the car then strike the tree? m/s Need Help? A baseball is hit so that it travels straight upward after being struck by the bat. A fan observes that it takes 2.90 s for the ball to reach its maximum height, Find the ball's initial velocity. m/s upward Find the height it reaches, m Need Help? The height of a helicopter above the ground is given by h = 3.25t3, where h is in meters and t is in seconds. At t = 1.95 s, the helicopter releases a small mailbag. How long after its release does the mailbag reach the ground? s Need Help?

Explanation / Answer

For the first, we will need to use a combination of D = delta(V^2)/2a and Vf = Vi+at. Using the D = delta(V^2)/2a, we get 60.1 = (vf^2-vi^2)/(2*-5.70). This can be re-written as -685.140 = vf^2-vi^2. Now we know vf = vi-5.70*4.3 so we can write vi = vf+5.7*4.3 or vi = vf+24.51. Plug this vi into the D equation to get -685.140 = vf^2-(vf+24.51)^2. When you solve this, you should get vf^2's canceling and -84.3999 = -49.020vf. Vf then comes out to be 1.7217 m/s

For 2nd part, set vi-9.8*2.9 equal to 0 since at max, velocity would be 0. This gives vi as 28.42 m/s.
As for height, use D = delta(V^2)/(2*-9.8) ---> D = (0^2 - 28.42^2)/(2*-9.8) = 41.21

For 3rd part, at t = 1.95, h = 24.0983 m. When released, the mailbag has no velocity so we have 0 = -24.0983 + 1/2*g*t^2 (set down as positive). This gives 24.0983 = .5*9.8*t^2. This gives t^2 = 4.918 and thus t = 2.2177

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