An insect jumps with an initial vertical velocity of 1.0 m s-1, reaching a maximum height of 3.5×10-2 m. Assume the deceleration is uniform.

Question 14

An insect jumps with an initial vertical velocity of 1.0 m s^-1, reaching a maximum height of 3.5×10^-2 m. Assume the deceleration is uniform.

What is the magnitude of the deceleration?

A 3.6 m s^-2                        B 9.8 m s^-2                        C 14 m s^-2                         D 29 m s^-2

Reference: Past Exam Paper – June 2015 Paper 11 Q8

Solution: 

Answer: C.

Initial velocity, u = 1.0 m s^-1

Maximum height reached, s = 3.5×10^-2 m

At the maximum height, the insect is momentarily at rest. Its velocity is zero. It cannot have a non-zero velocity as this would allow it to move further up and thus it cannot be called the ‘maximum’ height.

Final velocity, v = 0 m s^-1

v² = u² + 2as

0 = 1² + 2×a×(3.5×10^-2)

Acceleration a = - 1 / 2×3.5×10^-2

Acceleration a = - 14 m s^-2

Deceleration = 14 m s^-2