Mechanics | Relativity Answers

This is a follow up question.
Assume in my first scenario that astronauts on B and C are asleep and unaware of A during the initial acceleration but awake during the second acceleration when the force is applied to B to stop its motion in relation to A. Astronaut C and B should at that point believe that the clock in B is ticking slower than the clock in C since both witness the acceleration of B with respect to C. But this contradicts our previous answer that the clock in C is ticking slower than the clock in B and A.
The only remedy to this contradiction that I can see is that the clocks in all different bodies would have to be compared to the point in which all bodies were initially together.

A spring whose spring constant, k = 12 N/m, is compressed 0.3 m. How much energy is now stored in the compressed spring? (Only type in the value for the answer.) *

Two trains are travelling on parallel tracks. Imagine that you are travelling on Train A. Train A travels 12 m/s. Train B is travelling at 20 m/s in the same direction but on a different set of tracks. At the point when train B is passing train A, describe the speed and direction of the train B as it appears to you.

7. A particle is projected horizontally at 15ms-1 from height of 20m. Calculate the horizontal distance covered
by the particle just before hitting the ground (g = 10ms-2).

A human cannon ball to be ejected at a scarily fast velocity of 11 ms-1 at an angle of 43˚ to the horizontal. The plan is that the ‘volunteer’, Susie, will land in a large (deep) paddling pool, which needs to be strategically placed on the horizontal playing field. Ignoring any air resistance and using g = 9.8 ms-2, calculate: (3.1)


(a) time taken to reach her maximum height above the ground



(b) total time spent in the air


(c) horizontal distance to where the paddling pool should be placed


(d) Susie’s velocity as she (hopefully) hits the water.


(e) If the pool has to been placed on ground that is 2.5 m lower than the launch point, calculate her new splash-down velocity.

When P = 100N and F = 85N, the box accelerates. The mass of the box is 25kg. Calculate the acceleration of the box.

A force of 10 N gives an object an acceleration of 6 m/s2. What force will give the same object an acceleration of 18 m/s2.

A car is moving with a uniform velocity of 20 m/s in a direction mentioned in the figure. If car continues to move in the same direction for next 10 seconds.

What is the magnitude of acceleration?

If the observation deck of Washington monument is 158m above the ground.
How many king-sized candy bars, each supplying 1.4 MJ of source energy, must an 80 kg man consume to replenish the energy he expends in climbing the 825 stairs up to the observation deck?

A Mazda Miata (950 kg) is traveling 70 mph down the highway at 40 degrees S of E and F-150 truck (1700 kg) is merging on the highway traveling 53 mph. The merge lane joins the highway at 33 degrees N of E. Estimate the resultant direction in words the solve for it and resultant speed in this direction. Convert final speed to mph.