Due: Wednesday, October 18 2017 11:59PM via Blackboard Instructor: Dr. David Z.

Question

Due: Wednesday, October 18 2017 11:59PM via Blackboard Instructor: Dr. David Z. Jacome 28. In our Scientific Inquiry class, students decide to launch a projectile horizontally off the roof of our building that is 50.0 m above the level ground below. They intend to hit a target on a level area below, out 230 m fromthe base of the building. Use g = 9.80 m/sad ignore air resistance. (a) How long will the projectile fly until it hits the ground? (b) What initial horizontal velocity vo is needed so that the projectile hits the target? 29. An elevator together with its passenger's weights 5000 N. At a certain instant, the tension in its supporting cable is 6000 N. Determine the magnitude and direction of its instantaneous acceleration. 30. A 1300-kg car initially has a velocity of 22.2 m/s due south. It brakes to a stop over a 180-m distance. (a) What is the magnitude of the car's acceleration, in m/s (b) What average net force magnitude was necessary to stop the car? (c) Assuming the tires do not skid, what coefficient of static friction between tires and pavement is needed?

Explanation / Answer

28.

a)

consider the motion along the vertical direction

Voy = initial velocity = 0 m/s

a = acceleration = - 9.8 m/s2

t = time taken

Y = displacement = - 50 m

using the equation

Y = Voy t + (0.5) a t2

- 50 = 0 t + (0.5) (- 9.8) t2

t = 3.2 sec

b)

along the horizontal direction

X = horizontal distance travelled = 230 m

Vox = velocity along the horizontal direction = ?

using the equation

X = Vox t

230 = Vox (3.2)

Vox = 71.875 m/s

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