5. A physics student skis down a hill, accelerating at a constant 2.0 m/s2 If it

Question

5. A physics student skis down a hill, accelerating at a constant 2.0 m/s2 If it takes her 15 s to reach the bottom, what is the length of the slope? t (s) 6. A dog runs down his driveway with an initial speed of 5 m/s for 8 s, then uniformly increases his speed to 10 m/s in 5 s. a) What was his acceleration during the 2nd part of the motion? b) How long is the driveway? t (s) 7. A mountain goat starts a rock slide and the rocks crash down the slope 100 m. If the rocks reach the bottom in 5 s, what is their acceleration? t (s) 8. A car whose initial speed is 30 m/s slows uniformly to 10 m/s in 5 seconds a) Determine the acceleration of the car b) Determine the distance it travels in the 3rd second (t-2s to t-3s) t (s)

Explanation / Answer

5. initial velocity, v0 = 0 (starts from rest)

a = 2 m/s^2 and t = 15 s

d = v0 t + a t^2 /2

d = 0 + (2 x 15^2 /2 ) = 225 m

6. (a) vi = 5 m/s , vf = 10 m/s and t = 5 s

vf = vi + a t

a = 1 m/s^2

(B) d = (5 x 8) + ((5 x 5) + (1 x 5^2 /2 ))

d = 77.5 m

7. d = v0 t + a t^2 / 2

100 = 0 + a(5^2)/2

a = 8 m/s^2

8. (a) 10 = 30 + (5a)

a= - 4 m/s^2

(b) d2 = (30 x 2) + (-4 x 2^2 /2) = 52 m

d3 = (30 x 3)- (4 x 3^2 / 2) = 72 m

d23 = d3 - d2 = 20 m

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