A body moving with a velocity of 20 m/s begins to accelerate at 3 m/s2. How far does the body move in 5 seconds?
2 answers:
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Given parameters:
Distance to hardware shop = 5 miles
Time to reach hardware shop = 10 minutes
Time spent at the shop = 30 minutes
Average speed to customer home = 45 mph
Time taken for the travel = 20 minutes
Unknown:
Average speed of the contractor = ?
Solution:
Average speed is the total distance covered divided by the total time taken.
Average speed =
total distance = distance to hardware shop + distance to customer's home
We do not know the distance to customer's home but we have been given the speed and time, so we can find the distance.
Distance = speed x time
Convert the time to hrs and solve;
60 minutes = 1 hr
20 minutes = =
So, Distance = 45mph x = 15miles
Now;
Total distance = 5 + 15 = 20miles
Total time = time to reach hardware shop + time to reach customer's house
= 10 + 20
= 30 minutes
Convert the time from minutes to hrs;
60 minutes = 1hr
30 minutes = = 0.5hr
So;
Average speed = = 40mph
The average speed is 40mph
The speed of the rock at 20 m is 34.3 m/s
Explanation:
We can solve this problem by using the law of conservation of energy: the mechanical energy of the rock, sum of its potential energy + its kinetic energy) must be conserved in absence of air resistance. So we can write:
where :
is the initial potential energy
is the initial kinetic energy
is the final potential energy
is the final kinetic energy
The equation can also be rewritten as follows:
where:
m = 100 kg is the mass of the rock
is the acceleration of gravity
is the initial height
u = 0 is the initial speed (the rock starts at rest)
is the final height of the rock
v is the final speed when h = 20 m
And solving for v, we find:
Learn more about kinetic energy and potential energy here:
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