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A car of mass 1metric ton starts from re...

A car of mass `1metric` ton starts from rest and accelerates to a speed of `72km//h` in `20 sec`. It then moves with a constant velocity for `80 sec`. And is bought to rest in next `10 sec`, (figure). Caculate the force acting on the car from (i) 0 to `20 sec` (ii) 20 to `100 sec` (iii) 100 to `110 sec`

Text Solution

Verified by Experts

Here, `m=1` metric to `n=1000kg`
`u=0, v= 72km//h= (72xx1000m)/(60xx60s)=20m//s`
`t=20s`
(i) From 0 to `20sec`
`a=(v-u)/t= (20-0)/(20)= 1m//s^(2)`
`F=ma=1000xx1= 1000N`
(ii) From `20s` to `100s`
velocity of car is constant `=20m//s`
`:.` acceleration, a=0
F=ma=Zero
(iii) From `100s` to `110 s`
`u=20m//s, v=0, t=10 s`
`a=(v-u)/t=(0-20)/(10)= -2m//s^(2)`
`F=ma=1000(-2)= -2000N`
Negative sign for force opposing the motion of the body.
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