Question

1. A rock is falling off a cliff. The work that gravity performs on the rock is _____.

A) zero
B)positive
C)negative
2. The sunlight that reaches Earth is generated by a transformation of _____.
A) mechanical energy
B) atmospheric energy
C)chemical energy
D)nuclear energy
3.At a department store, a toy train travels on a loop of track of length 14 m. The coefficient of rolling friction between the train's wheels and the track is 0.10, and the weight of the train is 65 N. How much work does the train do against friction during each trip around the loop?
A) 91 J
B) 180 J
C) 41 J
D) 0 J
4. A ball is released out a window that is 13 m above the ground. How fast will the ball be traveling when it reaches the ground?
A) 0.26 km/s
B) 0 m/s
C) 16 m/s
D) 32 m/s
5.A tennis ball is released from a height of 3.7 m above the floor, and then bounces three times. With each bounce, dissipative forces cause it to lose 18.0% of its mechanical energy. How high does it reach after the third bounce?
A) 200 cm
B) 20 cm
C) 200 mm
D) 250 cm
6.At a certain point on the trackway, a roller coaster car has 27,000 J of potential energy and 132,000 J of kinetic energy. The value 159,000 J equals _____ of the coaster car at this point.
A) the total mechanical energy minus dissipated energy
B) the total mechanical energy plus dissipated energy
C) the total mechanical energy
D) the total internal and external energy
7.A car of mass 1290 kg is traveling along a horizontal road. During a span of 8.9 seconds, the car accelerates from 10.0 m/s to 16.5 m/s. How much work does the car's engine perform on the car during this time?
A) 791 kJ
B) 340 kJ
C) 692 kJ
D) 111 kJ

Answer 1

1). A rock is falling off the cliff so here in this case force of gravity will act downwards as well as it will displace downwards so here both are along same direction

When force and displacement both are along same direction so work done is always positive.

so here answer will be (B) POSITIVE

2). In case of sunlight the energy is produced on the surface of sun which is radiated in all directions

This energy is the result of nuclear reactions that occurs on the surface of sun

So answer will be (D) NUCLEAR ENERGY

3). Work done by friction is given as

`W = F_f * distance`

here we know that

`F_f = \mu (w) = 0.10 (65) = 6.5 N`

`distance = 14 m`

now work done is given as

`Work = 6.5 * 14 = 91 J`

4). A ball is released from 3.7 m

so here the speed of ball when it hit the floor is given as

`v_f^2 - v_i^2 = 2ad`

`v_f^2 - 0^2 = 2(9.8)(13)`

`v_f = 16 m/s`

5). Initial total potential energy of the ball is given as

`U = mgh`

`U = m(9.8)(3.7)`

in each bounce it loss 18% of its energy

So after each bounce the energy will be 82% of initial energy

so here we will have total energy after 3 bounce

`U_f = (0.82)(0.82)(0.82) m(9.8)(3.7) = 19.99m`

now the height will be

`h = (U)/(mg) = (19.99m)/(m(9.8))`

`h = 2.00 m = 200 cm`

6). given that

potential energy = 27,000 J

kinetic energy = 132,000 J

so here

KE + PE = 27000 + 132000 = 159000 J

so here sum of KE and PE is known as mechanical energy

(C) Mechanical energy

7) work done = change in kinetic energy

`W = (1)/(2)m(v_f^2 - v_i^2)`

`W = (1)/(2)(1290)(16.5^2 - 10^2)`

`W = 111 kJ`