Is my steps correct.pls help .thank you.
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It is incorrect because the question says the KE is reduced by 75% but your working shows that you have reduced speed by 75% . The reduction % in speed is what you need to find. Instead your end result is finding the % decrease in the KE.
Information from first line gives you:
KE = (1/2) mv2 (formula for kinetic energy and it shows the direct proportion relationship, ie,
when speed v increases, v2 increases, KE increases, when v decreases, v2
decreases, KE decreases.)
So second line says KE decreases by 75% of its original value,
This means new KE = 0.25 (1/2) mv2. ( (1/2)m is a constant, so you do not have to bother about it)
=> New KE = (0.5v)2 (1/2)m
=> New speed has decreased from v to 0.5v
So % of reduction in v is [(v-0.5v) / v] x 100% = 50%
The first attempt in the earlier solution, I made a mistake of skipping a step…so I took the reduction in v2 instead of v = speed.