The athlete Emily Davis won the 100 m sprint gold medal at London Olympic 2012 setting a new Olympic record of 10.54 s . Assume that she achieved her maximum speed in a very short time and subsequently ran the race with

Correct answer: A. -4900 J Mass of the athlete, m = 50 kg Acceleration due to gravity, g = 9.8 m/s^2 Weight of the athlete, W = mg = 50 × 9.8 = 490 N Average resistance force, f = (1)/(10) W = (1)/(10) × 490 = 49 N Displacement of the athlete, s = 100 m Since the resistance force acts in the direction opposite to the displacement, the angle between them is 180^ ^ ^ . Work done by the resistance, W_R = f s (180^ ^ ^ ) = -f s W_R = -49 × 100 = -4900 J

Concepts Of Physics MCQ Edition [Volume 1]

Exam: Concepts Of Physics MCQ Edition [Volume 1]
Subject: Physics
Chapter: Work and Energy

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Work and Energy

The athlete Emily Davis won the 100 m sprint gold medal at London...

The athlete Emily Davis won the

100 \text{ m}

sprint gold medal at London Olympic 2012 setting a new Olympic record of

10.54 \text{ s}

. Assume that she achieved her maximum speed in a very short time and subsequently ran the race with that speed till she crossed the line. Take her mass to be

50 \text{ kg}

. Assuming that the track, the wind etc. offered an average resistance of one tenth of her weight, calculate the work done by the resistance during the run.

Options

A $-4900 \text{ J}$
B $4900 \text{ J}$
C $-490 \text{ J}$
D $-5000 \text{ J}$

Correct answer

A. $-4900 \text{ J}$

Step-by-step solution

Mass of the athlete,

m = 50 \text{ kg}

Acceleration due to gravity,

g = 9.8 \text{ m/s}^2

Weight of the athlete,

W = mg = 50 \times 9.8 = 490 \text{ N}

Average resistance force,

f = \dfrac{1}{10} W = \dfrac{1}{10} \times 490 = 49 \text{ N}

Displacement of the athlete,

s = 100 \text{ m}

Since the resistance force acts in the direction opposite to the displacement, the angle between them is

180^{{}^{{}^{\circ}}}

.

Work done by the resistance,

W_R = f s \cos(180^{{}^{{}^{\circ}}}) = -f s

W_R = -49 \times 100 = -4900 \text{ J}

Practice Work and Energy on Quantrex Academy →

More from Work and Energy

A block of mass 2.00 kg travelling at a speed of 10.0 m/s accelerates at 3.00 m/s² for… Concepts Of Physics MCQ Edition [Volume 1]A box is pushed a distance of 4.0 m across a floor which offers a resistance of 100 N .… Concepts Of Physics MCQ Edition [Volume 1]The combined mass of a cyclist and the bike is 90 kg . Determine the increase in kinetic… Concepts Of Physics MCQ Edition [Volume 1]A block of mass 5.0 kg slides down an incline having an inclination of 30^ ^ ^ ∘ and a… Concepts Of Physics MCQ Edition [Volume 1]A stationary particle of mass 15 g is accelerated by a constant force of 2.50 N over a… Concepts Of Physics MCQ Edition [Volume 1]A particle travels from a position r _1 = (2 m) i + (3 m) j to a new position r _2 = (3… Concepts Of Physics MCQ Edition [Volume 1]A man travels along a straight horizontal road carrying a block of mass 2 kg in his hand.… Concepts Of Physics MCQ Edition [Volume 1]A particle is acted upon by a force F = a + bx in the x -direction, where a and b are… Concepts Of Physics MCQ Edition [Volume 1] Full Work and Energy list All Concepts Of Physics MCQ Edition [Volume 1] PYQs