Physics Answers

A 65.0-kg runner has a speed of 5.20 m/s at one instant during a long-distance

event. (a) What is the runner’s kinetic energy at this instant? (b) How much net

work is required to double his speed?

The force F = i + 3j + 2k acts at the point (1, 1, 1). (a) Find the torque of the force about the point (2, −1, 5). Careful! The vector r goes from (2, −1, 5) to (1, 1, 1)

A 85 Kg block of ice is being pushed in a straight rough road. The force exerted on the ice 300 N and acceleration of the entire system is 10 m/s^2. What is the friction force between the ice and the rough road.

4. A racer accelerates from rest at a constant rate of 2 m/s2. (a) How fast will the racer be going at the end of 6.0 s? (b) How far has the racer traveled during this time?

(Answer: a. 12 m/s & b. 36 m)

A scientist working late at night in her low-temperature physics laboratory decides to have a cup of hot tea, but discovers the lab hot plate is broken. Not to be deterred, she puts about 8.00 oz of water, at 12.0°C, from the tap into a lab dewar (essentially a large thermos bottle) and begins shaking it up and down. With each shake the water is thrown up and falls back down a distance of 31.3 cm.

 If she can complete 30 shakes per minute, how long will it take for the water to reach 77.1°C?

The makers of a certain automobile advertise that it will accelerate from 15 to 50 mi/hr in 13 s. What is the value of the initial velocity in m/s?

Redshift measurements show that a galaxy is moving away from the Earth at the speed of 60000 km/s. Taking the Hubble constant H, as 2.2 x 10-18 s-1 and 1 light-year as 1013 km, calculate and show your working for: a how far the galaxy is from the Earth

1. What is the rotational analog force?

a. angular momentum

b. angular velocity

c. moment of inertia

d. torque

A contractor uses a paddle stirrer to mix a can of paint. The paddle turns at 29.2 rad/s and exerts a torque of 17.1 N·m on the paint, doing work on the paint at a rate of Power = τω = 17.1 N·m × 29.2 rad/s = 499.3 W. An internal energy increase of 12.1 kJ causes the temperature of the paint to increase by 1.00 K.

If there were no heat flow between the paint and the surroundings, what would be the temperature change of the paint as it is stirred for 5.00 min?

How much work must be done to a proton to accelerate it from rest to 0.998c.