Three students have been studying relative motion and decide to do an experiment

Question

Three students have been studying relative motion and decide to do an experiment to demonstrate their knowledge. The experiment plan calls for Jane to drive her pickup in a straight line across the parking lot at a constant speed of 16.8 m/s. Fred is in the back of the truck and throws a baseball backward and upward at an angle ? out the back of the truck. Sue observes the flight of the ball while standing nearby in the parking lot.

(a) If Fred can throw the ball 34.4 m/s, at what angle relative to the horizontal should he throw the ball in order for Sue to see the ball travel vertically upward? (Enter your answer to at least one decimal place.)

(b) If Fred throws the ball at this angle, how high does Sue observe it to travel above the level at which it was thrown?

Explanation / Answer

a) if fred throws at an angle @ .
horizontal peed w.r.ttruck   = 34.4cos@ in opposite direction truck
w.r.t to ground = 34.4cos@ - 16.8
if horizonal compo= 0
it will travel vertically upoward w.r.t ground
cos@ = 16.8 / 34.4
@   = 60.78 degrees

b) speed in vertical = 34.4sin60.78
= 30 m/s

using v^2 - u^2 =2hg
0 - 30^2 =2 x(-9.8) x h
h = 45.92 m

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