If a ball is thrown vertically upwards with a velocity of `40m//s`, then velocity of the ball after `2s` will be `(g = 10m//s^(2))`
(a) `15m//s` (b) `20 m//s` (c) `25m//s` (d) `28 m//s`

Options

A. `15m//s`
B. `20 m//s`
C. `25m//s`
D. `28 m//s`

Answer

To solve the problem of finding the velocity of a ball thrown vertically upwards after 2 seconds, we can follow these steps:

### Step 1: Identify the Given Values
- Initial velocity (u) = 40 m/s (upwards)
- Time (t) = 2 s
- Acceleration due to gravity (g) = 10 m/s² (downwards)

### Step 2: Determine the Direction of Acceleration
Since the ball is thrown upwards, the acceleration due to gravity will act in the opposite direction (downwards). Therefore, we will take the acceleration (a) as negative:
- a = -g = -10 m/s²

### Step 3: Use the First Equation of Motion
The first equation of motion relates the final velocity (v), initial velocity (u), acceleration (a), and time (t):
\[ v = u + a \cdot t \]

### Step 4: Substitute the Values into the Equation
Now, we can substitute the known values into the equation:
\[ v = 40 \, \text{m/s} + (-10 \, \text{m/s}^2) \cdot (2 \, \text{s}) \]

### Step 5: Calculate the Result
Now, perform the calculations:
\[ v = 40 \, \text{m/s} - 20 \, \text{m/s} \]
\[ v = 20 \, \text{m/s} \]

### Step 6: Conclusion
The velocity of the ball after 2 seconds is 20 m/s.

### Final Answer
The correct option is (b) 20 m/s.

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