A particle is projected vertically upwards. What is the value of acceleration
(i) during upward journey,
(ii) during downward journey and
(iii) at highest point?

Answer

To solve the question regarding the acceleration of a particle projected vertically upwards, we will analyze the motion in three different scenarios: during the upward journey, during the downward journey, and at the highest point.

### Step-by-Step Solution:

1. **Acceleration During Upward Journey:**
- When the particle is projected upwards, the only force acting on it is the gravitational force, which is directed downwards.
- The gravitational force (weight) can be expressed as \( F = mg \), where \( m \) is the mass of the particle and \( g \) is the acceleration due to gravity (approximately \( 9.81 \, \text{m/s}^2 \)).
- The acceleration \( a \) of the particle can be calculated using Newton's second law:
\[ a = \frac{F}{m} = \frac{mg}{m} = g \]
- Therefore, the acceleration during the upward journey is \( g \) directed downwards.

2. **Acceleration During Downward Journey:**
- When the particle starts to fall back down, the same gravitational force \( F = mg \) acts on it.
- Again, using Newton's second law:
\[ a = \frac{F}{m} = \frac{mg}{m} = g \]
- Hence, the acceleration during the downward journey is also \( g \) directed downwards.

3. **Acceleration at the Highest Point:**
- At the highest point, the particle momentarily comes to rest before it starts descending. However, the gravitational force is still acting on it.
- The calculation remains the same:
\[ a = \frac{F}{m} = \frac{mg}{m} = g \]
- Thus, the acceleration at the highest point is also \( g \) directed downwards.

### Final Answers:
- (i) During upward journey: \( g \) (downwards)
- (ii) During downward journey: \( g \) (downwards)
- (iii) At highest point: \( g \) (downwards)