The US athlete Florence Griffith oyner won the 100 m spring gold medal at Seol Olympic 1988 setting a new Olympic record of 10.54s. Assume that she achieved her maximum speed in a very short time and then ran the race with that speed till she crossed the line. Take her mas ot be 50 kg. a. Calculate the kinetic energy of Griffith Joyner at her full speed. b. Assuming tht the track the wind etc. offered an average resistance of one tenth of her weight, cfalculate the work done by the resistsnce durng the run. c. What power Griffith Joyner had to exet ot maintain uniform speed?

Answer

A, B, C, D

Explanation

`S=100m, t=10.54sec, m=50kg`
Themotion can be assumed to be uniform because acceleration is minimum
a. `Speed v=S/t=9.487 m/s`
So K.E. `=1/2mv^2=2250J`
`b. Weight `=mg=490J`
`given R=(mg)/10=49J`
So, work done against resistance
`W_F=-RS=-49xx100`
`rarr W_(Ff)=-4900J` c. To maintain her uniform speed she has to exert 4900J of energy to overcome friction.
`P=W/t`
`=4900/1054=465W`