Chapter 2: Q13CQ (page 79)
Is it possible for speed to be constant while acceleration is not zero? Give an example of such a situation.
Short Answer
Yes, it is possible in the case of uniform circular motion.
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Chapter 2: Q13CQ (page 79)
Is it possible for speed to be constant while acceleration is not zero? Give an example of such a situation.
Yes, it is possible in the case of uniform circular motion.
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A helicopter blade spins at exactly revolutions per minute. Its tip isfrom the centre of rotation.
(a) Calculate the average speed of the blade tip in the helicopter’s frame of reference.
(b) What is its average velocity over one revolution?
a) Explain how you can use the graph of position versus time in Figure 2.54 to describe the change in velocity over time.
Identify
(b) the time ( ta, tb , tc , td , or te ) at which the instantaneous velocity is greatest,
(c) the time at which it is zero, and
(d) the time at which it is negative.

Figure 2.54
Conversations with astronauts on the lunar surface were characterized by a kind of echo in which the earthbound person’s voice was so loud in the astronaut’s space helmet that it was picked up by the astronaut’s microphone and transmitted back to Earth. It is reasonable to assume that the echo time equals the time necessary for the radio wave to travel from the Earth to the Moon and back (that is, neglecting any time delays in the electronic equipment). Calculate the distance from Earth to the Moon given that the echo time was 2.56 s and that radio waves travel at the speed of light ( 3 x 108m/s ).
(a) Sketch a graph of velocity versus time corresponding to the graph of displacement versus time given in Figure 2.55.
(b) Identify the time or times ( ta , tb , tc , etc.) at which the instantaneous velocity is greatest.
(c) At which times is it zero?
(d) At which times is it negative?

A soft tennis ball is dropped onto a hard floor from a height of \[{\bf{1}}.{\bf{50}}{\rm{ }}{\bf{m}}\]and rebounds to a height of\[{\bf{1}}.{\bf{10}}{\rm{ }}{\bf{m}}\]. (a) Calculate its velocity just before it strikes the floor. (b) Calculate its velocity just after it leaves the floor on its way back up. (c) Calculate its acceleration during contact with the floor if that contact lasts\[{\bf{3}}.{\bf{50}}{\rm{ }}{\bf{ms}}{\rm{ }}\left( {{\bf{3}}.{\bf{50}} \times {\bf{1}}{{\bf{0}}^{ - {\bf{3}}}}{\bf{s}}} \right)\]. (d) How much did the ball compress during its collision with the floor, assuming the floor is absolutely rigid?
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