If the force moving an object points at least partially in the opposite direction of the objects motion, the work is considered to be negative.
<u>Explanation:
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Work done is the measure of displacements caused on an object by the amount of force acting on it. The work done can be positive or negative. If the direction of force acting on an object is along the direction of motion of the object then the work done is positive.
This is because, in this case the external force is helping the object to continue its state of motion. So, if the force acting on the object is in completely opposite or partially opposite direction to the direction of motion of the object, it will stop or slow down the motion of the object.
This kind of force will have negative direction to the motion of the object and hence the work done will also be negative.
Answer:
Time of flight=3.5 seconds
Speed at maximum height is 0
Explanation:
Φ=60°
initial velocity=u=20m/s
Acceleration due to gravity=g=9.8 m/s^2
Total time of flight=T
Final speed=v
question 1:
T=(2 x u x sinΦ)/g
T=(2 x 20 x sin60)/9.8
T=(2 x 20 x 0.8660)/9.8
T=34.64/9.8
T=3.5 seconds
Question 2
Speed at maximum height is 0
Answer:3.95 m/s
Explanation:
Given
Initial velocity(u)
launch angle
Player is 53 m away
Range of projectile
R=41.02 m
so he need to run 53-41.02=11.98 m
Time of flight of projectile 
T=3.03 s
thus average speed of boy 
Answer:2200 hz
Explanation:
speed=242m/s
Distance between crest is there wavelength=0.11m
Frequency=speed ➗ wavelength
Frequency=242 ➗ 0.11
Frequency=2200
Frequency=2200 hz
