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1.A car goes off a cliff horizontally at 49 m/s and falls for 5 seconds
a. What us the vertical speed of the car after 5 seconds?
b. What is the horizontally speed of the car after 5 seconds ?
c. What is the actual speed of the car after 5 seconds ?

2.A golfer wants to drive a golf ball a distance of 120 m. If the 3-wood launches the ball at 12 degree above the horizontal. What must be the initial speed of the ball to achieve the required distance ?

3. A place kicker must kick a football from a point of 28 m from the goal and the ball must clear the crossbar, which is 3 m high. When kicked, the ball leaves the ground with a speed of 25 m/s at an angle of 45 degree to the horizontal.
a. By how much does the ball clear of fall short of clearing the crossbar?
b. Does the ball approach the crossbar while it still rising or falling ?
8. Flash throws a ball into the air as hard as he can and then runs as fast as he can under the ball in order to catch it. If his maximum speed in throwing the ball is 15 m/s and his best time for the 50 m distance is 5 seconds, how high does the ball raise and at what angle did he shoot i?

If you answer all these questions, your the best :O !



Answer :

AL2006
#1).  The horizontal speed doesn't change. 
The vertical speed is accelerated by gravity.

a).  Gravity increases the vertical speed by 9.8m/s every sec.
After 5 sec, the car is falling (5x9.8) = 49 m/s vertically.

b).  Horizontal:  49m/s !  Wow !  Almost 110 mph. No wonder he went off the cliff.
After 5 seconds, it's still 49 m/s.

c). After 5 sec, the horizontal speed and vertical-down speed are both 49 m/s.
The combination results in a velocity that points 45 degrees down from horizontal,
and its magnitude is

     square root of (49² + 49²) = 49 √2 = about 69.3 m/s .


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