Hi, i got a motor in which written Power = 40W , and supply Voltage 24V, 110RPM , i want to know what current will the motor draw under no load and with full load ? can ohm's law apply here I=P/V=40/24 = 1.6A ?
and another motor Vs=24V , 0.5 A , is its total power =12 watt or another number ?

thanks

YOu cannot apply ohm's law. THe only real way to figure it out is to measure it or have some other information about the motor's performance curves (speed, voltage, current, torque).

If you know the motor's resistance then you can use V=IR to find it's stall current. It's easy enough and safe enough to measure the no-load current (unlike measuring stall current where you have to clamp the motor's shaft).

Also, the wattages given are the motor's output power. YOu have no idea what it's efficiency is at that operating point so you can't even use P=IV to figure out the current it will draw since you don't know the efficiency.

Cant with just the motor power sepecified measure the drawen current ?
P=I*V ,P=40,V=24, then I=1.5A , then V=I*R , then R=16 ohm ... is this correct ?

I would start by measuring no-load current. This should be easy; no need to guess.

You can estimate the stall current by measuring the stalled current at reduced voltage (1V?) and scaling it to your intended supply. It's not linear, but it's an estimate.

I'll hazard a guess that the output power is the maximum (why advertise anything else?), which is near 50% load and 50% speed. So this means they probably got 40W at 55 rpm. But your motor will last a lot longer when you operate at less than 25% load (75% speed).

These are all techniques to get an approximation. These approximations may be off; so good engineering practice should govern your use of the data that you get.