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Explain briefly why the work done by a fielder when he takes a catch in a cricket match is negative.
1 J = ______ calorie.
A boy of mass 40 kg climbs up the stairs and reaches the roof at a height 8 m in 5 s. Calculate:
- the force of gravity acting on the boy,
- the work done by him against the force of gravity,
- the power spent by boy. (Take g = 10 m s-2)
The work done on an object does not depend on the :
A weight lifted a load of 200 kgf to a height of 2.5 m in 5 s. calculate: (i) the work done, and (ii) the power developed by him. Take g= 10 N kg-1.
State the energy changes which take place when A stone dropped from the top of a cliff reaches the ground after some time.
In the following case write yes, if the work is being done and no if no work is being done.
A boy climbing up a staircase.
(i) A 200g ball is thrown vertically upward with an initial velocity of 30 ms-1. Draw a velocity-time graph for the motion of ball.
(ii) How long will the ball take to reach the highest point?
(iii) What will be the kinetic energy of ball, when it returns to the starting point, neglecting the air resistance?
(iv) What will be the potential energy of ball at highest point?
State whether work is done or not, by writing yes or no, in the following case:
A boy climbs up 20 stairs.
