Question
If a ball is thrown vertically upwards with a velocity of $$40\,m/s,$$ then velocity of the ball after $$2\,s$$ will be $$\left( {g = 10\,\,m/{s^2}} \right)$$
A.
$$15\,m/s$$
B.
$$20\,m/s$$
C.
$$25\,m/s$$
D.
$$28\,m/s$$
Answer :
$$20\,m/s$$
Solution :
Here, initial velocity of ball $$u = 40\,m/s$$
Acceleration of ball $$a = - g\,m/{s^2} = - 10\,m/{s^2}$$
Time $$= 2s$$
From first equation of motion,
$$\eqalign{ & v = u + at \cr & v = 40 - 10 \times 2 \cr & \Rightarrow v = 20\,m/s \cr} $$
Here, initial velocity of ball $$u = 40\,m/s$$
Acceleration of ball $$a = - g\,m/{s^2} = - 10\,m/{s^2}$$
Time $$= 2s$$
From first equation of motion,
$$\eqalign{ & v = u + at \cr & v = 40 - 10 \times 2 \cr & \Rightarrow v = 20\,m/s \cr} $$
