– When answering questions, be sure to include as much relevant information in your answer
as possible
–Showing your units before, during, and after your calculation. If you get a velocity, it must be
in m/s etc.
–Give all numerical answers in scientific format if appropriate, i.e. 3E8m/s instead of
300000000m/s. Also, do not include unnecessary decimal places, i.e. if when calculating a
mass, you get an answer of 146.8863847kg, you should simply put 147kg, adding the
additional decimal places does not show meaningful accuracy.
QUESTIONS TO ANSWER:
1. The JWST will observe the sky in infrared wavelengths, using a much bigger mirror than HST.
Unlike HST, which orbits fairly close to Earth (559 km away), JWST will be sent into orbit quite
a bit further from Earth, at a distance of about 1.5 million km away from Earth. In fact, it is more
helpful to think about JWST orbiting the Sun than orbiting the Earth. While in orbit, JWST will
remain farther away from the Sun than the Earth is. JWST will keep up with the Earth as it orbits
the Sun, so that the Earth will always lie between JWST and the Sun, as in the Figure below.
Unlike HST, which orbits fairly close to Earth (559 km away), JWST will be sent into orbit quite
a bit further from Earth, at a distance of about 1.5 million km away from Earth. In fact, it is more
helpful to think about JWST orbiting the Sun than orbiting the Earth. While in orbit, JWST will
remain farther away from the Sun than the Earth is. JWST will keep up with the Earth as it orbits
the Sun, so that the Earth will always lie between JWST and the Sun, as in the Figure below.
While JWST is in orbit, the Earth will be at a distance of 1.494×109m from the telescope, and the
Sun will be 1.49598×1011m further away, in the same direction. The mass of the Sun is 1.9884×1030kg, the mass of the Earth is 5.945×1024kg, and the mass of JWST will be about 6500 kg.
Sun will be 1.49598×1011m further away, in the same direction. The mass of the Sun is 1.9884×1030kg, the mass of the Earth is 5.945×1024kg, and the mass of JWST will be about 6500 kg.
1.1 What is the gravitational force JWST will feel from the Sun (strength and direction)?
1.2 What is the gravitational force JWST will feel from the Earth (strength and direction)?
1.3 What is the total force JWST will feel from both the Earth and Sun?
2. What velocity will JWST have to have in order to keep up with the Earth in its orbit
around the Sun? In other words, what velocity will JWST have to have so that its orbital
period around the Sun is exactly one year (3.156×107s), just like the Earths orbital period
around the Sun?
2.1 What is the kinetic energy JWST will have as it orbits? Hint: Use the velocity you
calculated in the question above.
2.2 What is its gravitational potential energy with respect to the Sun only?