Concept explainers
(a)
The impulse athlete receives from the platform.
(a)
Answer to Problem 20P
The impulse athlete receives from the platform is
Explanation of Solution
Impulse experienced by the athlete is caculated from expression of impulse force law .
Write the expression for the impulse force law.
Here ,
Conclusion:
Substitute
Thus, the impulse athlete receives from the platform is
(b)
The velocity with which it reaches the platform.
(b)
Answer to Problem 20P
The velocity with which it reaches the platform is
Explanation of Solution
The athlete jumps on a plateform this converts potential energy to kinetic energy.
Write the expression for the conservation of energy.
Here
Write the expression for the initial kinetic energy.
Here,
Initially athlete jumps from the rest so initial velocity is zero.
Substitute
Write the expression for the initial potential energy.
Here,
Write the expression for the final kinetic energy.
Here,
Write the expression for the final potential energy.
Here,
Substitute
Substitute
Conclusion:
Substitute
Thus, the velocity with which it reaches the platform is
(c)
The velocity with which athlete leaves the platform.
(c)
Answer to Problem 20P
The velocity with which athlete leaves the platform is
Explanation of Solution
The athlete falls on the platform as a result impulse is produced.
Write the expression for the net impulse.
Here,
Write the expression for the impulse due to gravity.
Here,
Write the expression for the impulse momentum law.
Here,
Write the expression for the change in momentum.
Here,
Write the expression for the initial momentum.
Write the expression for the final momentum.
Substitute
Substitute
Substitute
Simplify the above equation for
Conclusion:
Substitute
Thus, the velocity with which athlete leaves the platform is
(d)
The height athlete jumps from the platform.
(d)
Answer to Problem 20P
The height athletes jumps from platform is
Explanation of Solution
The athlete jumps from the plateform to some height. Hence, kinetic energy is converted to gain potential energy.
Write the expression for the conservation of energy.
Here,
Write the expression for the initial kinetic energy at plateform .
Here,
Initially athlete jumps from the rest so initial velocity is zero.
Write the expression for the initial potential energy on platform.
Here,
Initial height at plateform is zero.
Substitute
Write the expression for the final kinetic energy at max height.
Here,
Substitute
Write the expression for the final potential energy at max height.
Here
Substitute
Simplify the above expression for value of
Conclusion:
Substitute
Thus, the height athletes jumps from platform is
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Chapter 9 Solutions
Physics for Scientists and Engineers with Modern Physics, Technology Update
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