The time needed is 25 s
Explanation:
Assuming that the sprinter is moving by uniform motion, then we can use the following equation that relates distance, time and speed:
where
v is the speed of the sprinter
d is the distance covered
t is the time elapsed
In this problem, we know that
v = 4 m/s is the speed of the sprinter
d = 100 m is the distance that must be covered
Solving for t, we find the minimum time needed:
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A single pulley has no advantage in reducing force. A single pulley only helps by changing direction of effort, pulling something from up to down feels easier then vice versa due to our muscles arrangement. However, the force needed is the same.
Meanwhile multiple pullies divide the tension. The lower pulley itself reduces the force into half so as to you feel a part of the tension while rest is suspended by the ceiling in the case in the diagram below.
Answer:
3.25 seconds
Explanation:
It is given that,
A person throws a baseball from height of 7 feet with an initial vertical velocity of 50 feet per second. The equation for his motion is as follows :
Where
s is the height in feet
For the given condition, the equation becomes:
When it hits the ground, h = 0
i.e.
It is a quadratic equation, we find the value of t,
t = 3.25 seconds and t = -0.134 s
Neglecting negative value
Hence, for 3.25 seconds the baseball is in the air before it hits the ground.
Assuming the driver starts slamming the brakes immediately, the car moves by uniformly decelerated motion, so we can use the following relationship
(1)
where
a is the deleceration
S is the distance covered after a time t
is the velocity at time t
is the initial speed of the car
The accident is 80 m ahead of the car, so the minimum deceleration required to avoid the accident is the value of a such that S=80 m and
(the car should stop exactly at S=80 m to avoid the accident). Using these data, we can solve the equation (1) to find a:
And the negative sign means it is a deceleration.