MathRevolution
One ball will drop from a certain height. The height it will reach after rebounding from the floor is 60 percent of the previous height. The total travel is 292cm when it touches the floor on third time. What is the value of the original height?
A. 80cm
B. 90cm
C. 100cm
D. 120cm
E. 130cm
*An answer will be posted in 2 days.
Hi,
we have to be careful to calculate the distance covered....
two ways..
1) let the distance be x...so first time it touches the floor - D = x...
next time it touches the floor, it travels .6x up and down - D = x+2*0.6x = 2.2x...
third time it touches the floor, it travels 0.6*0.6x up and down - D = 2.2x+2*0.6*0.6x = 2.92x...
so 2.92x = 292 ..... x =100
2) substitution..start from middle value..
initial height = 100...
so in next jump it goes up 100*0.6 = 60 and in the third it moves 60*0.6 = 36..
so distance covered = 100+2*60+2*36 = 292..
this is what we are looking for..