A rocket of mass 30 000 kg sits on a launch pad on the Earth’s surface. The rocket motors provide an upward force of 330 kN on the rocket.

Question 8

A rocket of mass 30 000 kg sits on a launch pad on the Earth’s surface. The rocket motors provide an upward force of 330 kN on the rocket.

What is the initial acceleration of the rocket?

A 0.12 m s^-2                      B 1.1 m s^-2                        C 1.2 m s^-2                        D 11 m s^-2

Reference: Past Exam Paper – November 2015 Paper 13 Q11

Solution:

Answer: C.

The forces acting on the rocket are its weight and the upward force provided by the rocket motors.

Weight of rocket = mg = 30 000 × 9.81

Weight = 294 300 N

The initial acceleration is provided by the resultant of the two forces.

Resultant force = ma

Upward force – Weight = ma

330 000 – 294 300 = 30 000 a

Acceleration a = 35 700 / 30 000 = 1.19 m s^-2 ≈ 1.2 m s^-2