Question

A car moving at 10 ms${}^{-1}$ skids for 2 m with locked brakes before coming to rest. How far will it skid if its speed is 20 ms${}^{-1}$?

• A. 6 m
• B. 10 m
• C. 8 m
• D. 12 m

Answer 1

The correct option is C 8 m

Given :
u = 10 ms${}^{-1}$ ; v = 0 ms${}^{-1}$ ; s = 2 m

Using Work-energy theorem,
1/2 mv${}^2$ - 1/2 mu${}^2$ = F x s

For case (1) :
=> 1/2 m(0)${}^2$ - 1/2 m (10)${}^2$ = F x 2
=> -1/2 m (100) = 2F
=> -25 m = F
=> m = - F / 25........(1)

For case (2) :
=> 1/2 m(0)${}^2$ - 1/2 m (20)${}^2$ = F x s
=> -1/2 m (400) = F x s
=> - 200 m = F x s........(2)

Substituting the value from (1) into (2),
=> - 200 x (- F/25) = F x s
=> 8 F = F x s
=> s = 8 meters