The x and y co-ordinates of a particle at any instant are `x = 4t^2` + 7t and y = 5t where x, y are in metres and in seconds. The acceleration at t=5s is :

Options

A. Zero
B. 20 `m s^(-2)`
C. 8 `m s^(-2)`
D. 40 `m s^(-2)`

Answer

c

Explanation

Here a=`sqrt(a_(x)^(2)+a_(y)^(2))` But `a_(y)=0`
`( :.(d^2y)/(dt^(2))=0)` and `a=a_(x)=(d^(2)x)/(dt^(2))=8 m s^(-2)`
For any value of .t.