A body mass 1 kg is thrown upwards with velocity 20 ms-1. It momentarily comes to rest after attaining a height of 18 m. How much energy is lost due to air friction? (g = 10 ms-2)
20 J
30 J
40 J
40 J
A.
20 J
The energy lost due to air friction is equal to the difference of initial kinetic energy and final potential energy.
Initially, body possess only kinetic energy and after attaining a height the kinetic energy is zero.
Therefore, loss of energy = KE - PE
=
The figure shows elliptical orbit of a planet m about the sun S. The shaded are SCD is twice the shaded area SAB. If t1 is the time for the planet to move from C to D and t2 is the time to move from A to B then,
t1 > t2
t1 =4 t2
t1 = 2t2
t1 = 2t2
C.
t1 = 2t2
Apply Kepler's law of area fo planetary motion.
The line joining the sun to the planet sweeps out equal areas time interval ie, areal velocity is constant.
Assuming the sun to have a spherical outer surface of radius r, radiating like a black body at a temperature to C, the power received by a unit surface (normal to the incident rays) at a distance R from the centre of the sun is :
D.
From Stefan's law, the rate at which energy is radiated by sun at its surface si
P = σ x 4 πr2T4
A roller coaster is designed such that riders experience " weightlessness" as they go round the top of a hill whose radius of curvature is 20 m. The speed of the car at the top of the hill is between
14 m/s and 15 m/s
15m/s and 16 m/s
16 m/s and 17 m/s
16 m/s and 17 m/s
A.
14 m/s and 15 m/s