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Rabbit kim
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A ball is thrown with enough speed straight up so that it is in the air several seconds. (a) what is the velocity of the ball when it gets to its highest point?
b) what is its velocity 1 s before it reaches its highest point?
c) what is the change in its velocity during this 1-s interval?
d) What is the velocity 1 s after it reaches its highest point?
e) what is the change in velocity during this 1-s interval?
f) what is the change in velocity during the 2-s interval? (careful!)
g) what is the acceleration of the ball during any of these time intervals and at the moment the ball has zero velocity?
My answer:
(a). The velocity of the ball is 0m/s when it reaches its highest point as at this time its upwards velocity would stop and its downward velocity would start occurring because gravity would completely reduce the speed of the ball to zero.
(b). Its velocity 1s before it reaches its highest point
= Its velocity 1s after it reaches its highest point- acceleration due to gravity*time of 1s before it reaches its highest point
= [0-(-9.8)*1]m/s
= 9.8m/s
(c). The change in its velocity during this 1s interval
= Its final velocity at the beginning of this 1s interval 1s-Its initial velocity at the end of this 1 interval
= (0-9.8)m/s
= -9.8m/s
It is negative since it slowed down as its velocity is decreased.
(d). Its velocity 1s after it reaches its highest point
= Its initial velocity 1s before it reaches its highest point+ acceleration due to gravity*time of 1s taken to reach its highest point
= 0+(-9.8)*1
= -9.8m/s
It is now negative because it moves down after the highest point.
(e).
The change in its velocity during this 1s interval
= Its velocity at the beginning of this 1s interval- Its initial velocity at the end of this 1 interval
= (-9.8-0)m/s
= -9.8m/s
(f). The change in its velocity during the 2s interval
= Its velocity at the beginning of this 2s interval- Its initial velocity at the end of this 2s interval
= (-9.8-9.8)m/s
= -19.6m/s
(g). The acceleration of the ball is 9.8ms^(-2) during any of these time intervals and at the moment the ball has zero velocity.
Also need help with this question:
A 60kg skydiver moving at terminal speed falls 50m in 1s. What power is the skydiver expanding on the air?
b) what is its velocity 1 s before it reaches its highest point?
c) what is the change in its velocity during this 1-s interval?
d) What is the velocity 1 s after it reaches its highest point?
e) what is the change in velocity during this 1-s interval?
f) what is the change in velocity during the 2-s interval? (careful!)
g) what is the acceleration of the ball during any of these time intervals and at the moment the ball has zero velocity?
My answer:
(a). The velocity of the ball is 0m/s when it reaches its highest point as at this time its upwards velocity would stop and its downward velocity would start occurring because gravity would completely reduce the speed of the ball to zero.
(b). Its velocity 1s before it reaches its highest point
= Its velocity 1s after it reaches its highest point- acceleration due to gravity*time of 1s before it reaches its highest point
= [0-(-9.8)*1]m/s
= 9.8m/s
(c). The change in its velocity during this 1s interval
= Its final velocity at the beginning of this 1s interval 1s-Its initial velocity at the end of this 1 interval
= (0-9.8)m/s
= -9.8m/s
It is negative since it slowed down as its velocity is decreased.
(d). Its velocity 1s after it reaches its highest point
= Its initial velocity 1s before it reaches its highest point+ acceleration due to gravity*time of 1s taken to reach its highest point
= 0+(-9.8)*1
= -9.8m/s
It is now negative because it moves down after the highest point.
(e).
The change in its velocity during this 1s interval
= Its velocity at the beginning of this 1s interval- Its initial velocity at the end of this 1 interval
= (-9.8-0)m/s
= -9.8m/s
(f). The change in its velocity during the 2s interval
= Its velocity at the beginning of this 2s interval- Its initial velocity at the end of this 2s interval
= (-9.8-9.8)m/s
= -19.6m/s
(g). The acceleration of the ball is 9.8ms^(-2) during any of these time intervals and at the moment the ball has zero velocity.
Also need help with this question:
A 60kg skydiver moving at terminal speed falls 50m in 1s. What power is the skydiver expanding on the air?