physics mid term 3

Hope probe moves around Mars in a circular orbit with a constant radius. How much work is done by the gravitational force on it?

• Fg · d

• -Fg · d

• mgh

• zero

Which is NOT a unit of kinetic energy?

• Joule

• Kg·m²/s²

• N (Newton)

• Kg·m²/s²

If the system does work on the external world, then its energy will:

• Increase

• Decrease

• Stay the same

• Be maximum

One joule of energy transferred in one second is:

• Volt

• Newton

• Calorie

• Watt

A weightlifter exerts 294 J of work to lift a weight by 0.6 m. What is the mass being lifted?

• 5.0 kg

• 100 kg

• 50 kg

• 490.0 kg

An electric motor lifts an elevator 6.0 m in 10.0 s by exerting an upward force of 3.20×10⁴ N. What power does the motor produce in kW?

• 19.2 kW

• 1920 kW

• 19200 kW

• 13×10⁵ kW

Ahmed pulls a box across a room as shown in the figure for 15m then he lifted it to 3m high, Find the following:

a. How much work does Ahmad do on the box through the first 15m?
b. How much work does Ahmad do on the box to lift the box?
c. Calculate the total work done on the box?

A 1000 kg car speeds up from 5m/s to 20m/s through 60m.

1. Calculate the work done by engine of the car?

2. Calculate the force of engine.

An object is thrown straight up. When is the work done by gravity on the object positive?

• when it is moving up

• when it is moving down

• when it is moving up or down

• It is always negative

What is the equivalent of 1 joule?

• 1 N/m

• 1 kg·m/s²

• 1 N·m

• 1 W·s