Question

An object is thrown vertically upwards with an initial velocity of 10 m/s. How long will it take for the object to return to its starting point?

• A. 2 seconds
• B. 1 second
• C. 3 seconds
• D. 5 seconds

Hint:

For vertical motion under gravity, the time taken to return to the starting point is twice the time taken to reach the highest point.

Answer 1

The Correct Option is A

When an object is thrown vertically upwards, it decelerates due to gravity until it reaches the highest point, and then accelerates downwards with the same magnitude of acceleration.
Step 1: The initial velocity of the object is \( u = 10 \, \text{m/s} \), and the acceleration due to gravity is \( g = 9.8 \, \text{m/s}^2 \).
Step 2: The time taken to reach the highest point can be calculated using the formula: \[ v = u - g t \] At the highest point, the final velocity \( v = 0 \), so: \[ 0 = 10 - 9.8 t \] \[ t = \frac{10}{9.8} \approx 1.02 \, \text{seconds} \]
Step 3: The total time for the object to return to its starting point is twice the time taken to reach the highest point: \[ \text{Total time} = 2 \times 1.02 = 2.04 \, \text{seconds} \] Thus, the correct answer is 2 seconds (approximately).