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YOUR PARTICIPATION FOR THE GROWTH OF PHYSICS REFERENCE BLOG

Monday, September 2, 2019

The nearest star to the Sun is Proxima Centauri. This star has a mass of


Question 5
(a) Define gravitational field strength. [1]


(b) The nearest star to the Sun is Proxima Centauri.
This star has a mass of 2.5 × 1029 kg and is a distance of 4.0 × 1013 km from the Sun.
The Sun has a mass of 2.0 × 1030 kg.

(i) State why Proxima Centauri may be assumed to be a point mass when viewed from the Sun. [1]

(ii) Calculate
1. the gravitational field strength due to Proxima Centauri at a distance of 4.0 × 1013 km, [2]
2. the gravitational force of attraction between the Sun and Proxima Centauri. [2]

(c) Suggest quantitatively why it may be assumed that the Sun is isolated in space from other stars. [2]
 [Total: 8]





Reference: Past Exam Paper – November 2016 Paper 42 Q1





Solution:
(a) Gravitational field strength is defined as the (gravitational) force acting per unit mass. 


(b)
(i)
The radius/diameter/size of Proxima Centauri is much less than the separation (of the Sun and the star (Proxima Centauri)). (Separation = 4.0 × 1013 km)

OR
(because) it is a uniform sphere


(ii)
1.
field strength = GM / x2
{distance should be in metre.}
field strength = (6.67×10-11 × 2.5×1029) / (4.0×1013 × 103)2
field strength = 1.0 × 10-14 N kg-1                         

2.
{Force = mg}
force = field strength × mass
force = 1.0×10-14 × 2.0×1030  

or
force = GMm / x2
force = (6.67×10-11 × 2.5×1029 × 2.0×1030) / (4.0×1013 × 103)2
force = 2.0 × 1016 N

(c)
The force (of 2 × 1016 N) would have little effect on the (large) mass of the Sun and would cause a negligible acceleration (of 1.0 × 10–14 m s–2).

OR
Many stars are all around the Sun. The net effect of the forces/fields is zero.

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